THE MICROSCOPIC ANATOMY OF THE INNER EAR OF THE DOG Thesis for tho Dogm of M. S. MICHIGAN STATE UNIVERSITY Murdina D. Thomas 1962 m'r LIBRARY Michigan State University THE MICROSCOPIC ANATOMY OF THE INNER EAR OF THE DOG BY Murdina D. Thomas A THESIS Submitted to the College of Veterinary Medicine of Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Anatomy 1962 ACKNOWLEDGEMENT The author wishes to express her sincere appreciation and gratitude to Dr. T. W. Jenkins, Department of Anatomy, for his guidance, unfailing supervision, and understanding of the problems involved. Appreciation is also due to Dr. M. Lois Calhoun, Pro- fessor and Head of the Department of Anatomy, for her understanding of the problem and for her encouragement in completing this manuscript. Thanks are also due to Dr. Esther M. Smith, Department of Anatomy, for her help in preparation of the plates. The author also wishes to thank Dr. M. B. Bharadwaj, of the Department of Anatomy for his advice concerning the manuscript, and also to express her sincere appreciation to Mrs. Esther Colby for her help in preparation of the microscopic sections. Lastly, the author wishes to express thanks to those members of the faculty and staff who so graciously have contributed suggestions and assistance, and to Mr. Andrew S. Moore for his help in the photography. ii r. ,__._.__.._-. ...., .. , TABLE OF CONTENTS Page INTRODUCTION . . . . . . . . . . 1 ANATOMY OF THE INNER EAR . . . . . 8 VESTIBULAR PORTION OF INNER EAR . . . lO Semicircular Canals lO Utriculus or Utricle l4 Sacculus or Saccule l6 Cupula 18 Endolymphatic Duct 18 Endolymph and Perilymph l9 Vestibular Nerve and Vestibular Ganglion 21 AUDITORY PORTION OF THE INNER EAR . . . 22 Osseous Spiral Lamina 27 Scala Media or Cochlear Duct 27 Vestibular or Reissner's Membrane 28 Basilar Membrane 28 Spiral Ligament 29 Stria Vascularis 3O Modiolus 31 Organ of Corti 31 Tectorial Membrane 32 Limbus Spiralis 33 Internal Spiral Sulcus 35 External Spiral Sulcus 35 Border Cells 35 Inner and Outer Pillar Cells 35 Tunnel of Corti 36 Inner Phalangeal Cells 35 Outer Phalangeal Cells 37 Cells of Hensen 37 Cells of Claudius 38 Cells of Boettcher 38 Sensory Hair Cells of the Organ of Corti 38 39 Cochlear Nerve and Spiral Ganglion iii MATERIALS AND METHODS RESULTS AND DISCUSSION . . . . . . . . VESTIBULAR PORTION OF THE INNER EAR Semicircular Canals Utriculus or Utricle Sacculus or Saccule Cupula Vestibular Nerve and Vestibular Ganglion AUDITORY PORTION OF THE INNER EAR Osseous Spiral Lamina Scala Media or Cochlear Duct Vestibular or Reissner's Membrane Basilar Membrane Spiral Ligament Stria Vascularis Modiolus Organ of Corti Tectorial Membrane Limbus Spiralis Internal Spiral Sulcus External Spiral Sulcus Border Cells Inner and Outer Pillar Cells Tunnel of Corti Inner Outer Cells Cells Cells Inner Cochlear Nerve and Spiral Ganglion Phalangeal Cells Phalangeal Cells of Hensen of Claudius of Boettcher and Outer Hair Cells SUMMARY AND CONCLUSIONS . . . . . LITERATURE CITED . iv Page 41 45 45 45 48 50 51 51 52 52 53 54 55 56 58 59 59 6O 61 62 63 63 63 64 64 64 65 65 65 66 67 69 71 Figure LIST OF DIAGRAMS Frontal section of the head of the dog through the external auditory meatus showing its relation to the structures of the middle and internal ear. This shows how the tem- poral bone was oriented in order to obtain the histological sections used in this study . . . . . . . . . . . . The membranous labyrinth of the inner ear of the dog showing the vestibular and auditory mechanisms and their nervous in— nervations. The osseous labyrinth has been removed in order to illustrate clearly the parts of the membranous labyrinth . . . . . A horizontal section through the inner ear of the dog showing the semicircular canals, superior and inferior vestibular ganglia, facial nerve, three and one-fourth coils of the cochlea, and the cochlear nerve . . A cross section through the organ of Corti of the first coil of the cochlea of the dog . . . . . . . . . . . . Page 24 Plate II. III. IV. VI. VII. VIII. IX. XI. XII. XIII. XIV. LIST OF PLATES Dorsal and caudal semicircular canals with cristae in relation to the utricle . . . Ampulla of dorsal semicircular canal show— ing crista . . . . . . . . . . Crista of dorsal semicircular canal . Crista of dorsal semicircular canal showing slope of organ . . . . . . . . . . . Caudal semicircular canal showing crista sacculus and caudal semicircular Utricle, canal . . . . . . . . . . . . Macula utricle . . . . . . . . . . . . . Part of brain and inner ear showing vestibular nerve . . . . . . . . . . Vestibular ganglion . . . . . . . . . . . . Osseous spiral lamina . . . . . . . . . . Osseous spiral lamina with cochlear nerve. Cochlear duct and its parts . . . . . . . Modiolus . . . . . . . . . . . . Organ of Corti . . . . . . . . . Part of brain and ear of dog showing cochlear nerve . . . . . . . . . . . . . . vi Page 73 75 77 79 81 83 85 87 89 91 93 95 97 99 101 INTRODUCTION The histological details of the inner ear of man can be readily found in the literature or in almost any text— book of histology. It is also possible to find available references for certain species which are commonly used as laboratory animals, e.g. guinea pig, Guild (1927), Lurie and Nachlas (1951), Smith §£_al, (1954), Wersall (1954), and Wersall (1956). In spite of the fact that the dog is so commonly used as an experimental laboratory animal, there are no available references to the microscopic anatomy of the inner ear (labyrinth) of this animal. The purpose of this study is to present the micro- scopic anatomy of the inner ear of the dog. There are many microtechnique problems encountered by anyone who attempts a histological study of the mammalian inner ear. There are few areas in the body where extremely delicate and complicated tissue such as neuroepithelium is in close apposition with bone. There are many stimula— ting challenges in preparing good slides of the inner ear. FIGURE A Frontal section of the head of the dog through the external auditory meatus showing its relation to the structures of the middle and internal ear. This shows how the temporal bone was oriented in order to obtain the histological sec- tions used in this study. omqmmbwwI—J N H H [.1 H [.4 [—1 [—0 H H [—1 0 to 00 \l 0 U1 b to N l—J .O O O O O O O 0 O 21. 22. 23. External auditory meatus Tympanic membrane Tympanic cavity Stapes in oval window Round window Ossicles Eustachian tube Vestibule Utricle Ampulla of semicircular canal Saccule Dorsal semicircular canal Caudal semicircular canal Endolymphatic duct Endolymphatic sac Cerebral dura Scala tympani Cochlear duct Scala vestibuli First coil of cochlea Second coil of cochlea Third coil of cochlea One-fourth coil of cochlea a1 ... . ... 4. O . . ”mu-«ac «MEN... FIGURE B The membranous labyrinth of the inner ear of the dog and the nervous innervations. The osseous labyrinth has been removai in order to illustrate clearly the parts of the membranous labyrinth. In the dOg the dorsal semicircular canal is the longest, the lateral canal is intermediate, and the caudal canal the shortest. The cochlea of the dog has three and one-fourth coils. Dorsal semicircular canal Lateral semicircular canal Caudal semicircular canal Dorsal ampullary nerve Lateral ampullary nerve Caudal ampullary nerve Utricle Saccule \omflmmngH Utricular nerve .....n O . Saccular nerve H H Cochlear duct [—1 N Coil one H LA) Coil two '_I 4:. Coil three H U1 Coil one—fourth H m Caecum cupulare l.._l \I O Caecum vestibulare I—‘ (I) Cochlear nerve andtk remaz anous is the audal and \.‘ - v I a \ \I /l .- "\n.\\" \S’: '-. /'..... sf ”94 64'?th if an . FIGURE C Diagram of a horizontal section through the inner ear of the dog, showing the semicircu inferior vestibular ganglia, fourth coils of the cochlea, o I—' I—' l—" H |-—' |-' |-" I—" H S (p ~4 ow u: p c» p) F'.P o o O . ' ' . lar canals, superior and facial nerve, three and one- and the cochlear nerve. Dorsal semicircular canal Lateral semicircular canal Caudal semicircular canal Oval window Caudal ampullary nerve Dorsal ampullary nerve Superior saccular nerve Major saccular nerve Cochlear vestibular ramus Superior vestibular ganglion Inferior vestibular ganglion Facial nerve Cochlear nerve Scala tympani Scala vestibuli Cochlear duct Spiral ganglion Utricular nerve Lateral ampullary nerve ner ear of rior and 2e and one- zen/e. /1 mm REVIEW OF LITERATURE INCLUDING THE ANATOMY OF THE INNER EAR A careful review of the literature indicates that a small amount of work has been done on the inner ear of the dog. Most of the investigations have been carried out on the inner ear of guinea pig, cat, and man. There is a very limited amount of literature and what there is is invariably tied up with the gross and microscopic anatomy that it seems advisable to combine the literature review with the anatomy of the inner ear. The inner ear is located in the petrous temporal bone and receives stimulation resulting in hearing and equilibrium. The semicircular canals contain the end organs of the vesti- bular nerve which comprise the mechanism for orientation of the body in space. The cochlea embodies the end organ of the cochlear nerve which conducts auditory impulses. These two parts along with the utricle and saccule comprise the mem— branous labyrinth. The osseous labyrinth is the structure carved out in the petrous temporal bone and has similar archi- tecture to that of the membranous labyrinth. The membranous labyrinth is suspended in the osseous labyrinth by means of connective tissue trabaculae which extend from the periosteum 8 of the osseous labyrinth to the walls of the membranous labyrinth (Figure A). In some places the membranous labyrinth is close to the periosteum of the osseous wall with which its connective tissue blends. However, for the most part it lies sus- pended in the perilymph by connective tissue trabaculae. The walls of the membranous labyrinth have a thin outer tunica propria and an inner simple squamous epithelial lining except in the region where neuro-epithelium is found. The tunica propria consists of delicate connective tissue fibers and stellate shaped fibroblasts. The wall of the membranous labyrinth is modified in certain regions to form sensory areas. In these regions, the epithelium is more complex and the fibers of the cochlear nerve terminate among the epithelial cells. There are six such neuroepithelial areas in each inner ear: the maculae utricli; the maculae sacculi; the cristae ampul- lares of the three semicircular canals; and the organ of Corti in the cochlear duct (Figures B and C). t al, (1956) stated that in the dog the laby— Getty rinth is about 15 mm. long and is incompletely divided into three compartments: cochlea, vestibule, and semicircular canals. Phylogenetically the vestibule is the oldest part 10 of the inner ear and in primitive vertebrates it consists of a fluid filled capsule in which branches of the vestibu— lar nerve are distributed. The vestibule is the chief end organ for proprioception. THE VESTIBULAR PORTION OF THE INNER EAR l. The Semicircular Canals (Figures A, B, C) The three semicircular canals in man are described as: a. External or lateral b. Anterior or superior c. Posterior Getty gt_§l, (1956) classified the canals of the dOg as lateral, dorsal, and caudal. Maximow and Bloom (1957) stated that in man the lateral canal is the shortest, the posterior the longest, and the superior is intermediate in length. Getty §§_§l, (1956) said the lateral canal is intermediate in length forming an arc measuring about 4 mm., the dorsal canal is the longest forming an arc measuring 6 mm. across the widest part, while the arc of the caudal canal is the smallest measuring only 3.5 mm. in medium sized dogs. These measurements vary with the size of the dog. One end of each canal is enlarged into a structure called the ampulla. The ll three semicircular canals communicate with the utricle through five openings. These canals are filled with a fluid, endolymph, and the ampullated end of each canal contains the crista or "little crest.” Each crista is covered by a gelatinous substance called the cupula (which is considered by some to be a fixation artifact). Hair tufts from the crista project into the cupula. The crista is stimulated by any change in the rate of movement or any form of sudden movement of the head. Wersall (1956) made an extensive study on the crista ampullaris of the guinea pig with both light and electron microscopy. He concluded that the crista occupies one- third of the diameter of the ampulla. The greater part of the crista is covered with sensory epithelium which changes in the lateral periphery of the organ to columnar or low cuboidal supporting epithelium. The connective tissue stroma of the crista contains few cells and a large number of nerve fibers which traverse the connective tissue to reach the epithelium and ramify in it. The sensory epithelium consists of two types of cells classified as sensory or hair cells and supporting or sus- tentacular cells. The hair cells are classified as type 1 12 and type 11. The type 1 cells are described as being bottle shaped with rounded bases and short slender necks. These cells extend throughout the distal two-thirds of the epi- thelium and do not extend all the way to the basement mem— brane. The hair cells are bounded apically by a cuticular plate through which hairs penetrate. Wersall (1956) stated that each type 1 hair cell is innervated by a nerve calyx which envelops it like a shell. Immediately beneath the cell membrane, is a zone of contact between the hair cells. There is an increase in the density of the cytoplasm in this region thus forming a terminal bar. The type 1 hair cells are most densely distributed in the central region of the crista and decrease in number towards the periphery of the organ. The type 11 hair cells were first described by Wersall in 1954. This type of hair cell is cylindrical in shape and has rounded bases in contrast to the bottle neck type 1 hair cells. Most of the type 11 hair cells are located in the lateral periphery of the crista. These cells are taller than the type 1 and often extend throughout the thickness of the epithelium all the way from the basement membrane. The type 11 hair cells vary in shape and size. Wersall (1954) stated that the two types of hair cells are innervated in a different way and thus each type of 13 cell is believed to have different functions. The stimu- lation of a type 1 hair cell results in reaction in one nerve fiber only, while the stimulation of a type 11 cell produces activity in several nerve fibers. The type 1 hair cells therefore represent a higher degree of sensitivity than the type 11 cells. The supporting cells of the crista are located through- out the sensory epithelium and are more numerous than the sensory hair cells. The supporting cells extend from the basement membrane to the surface of the crista. They have microvilli on their apical surfaces. The large oval nuclei are located in the base of the cells. The nuclear material contains a large number of granules and two dark staining nucleoli. Each crista is innervated by separate myelinated nerve fibers varying in diameter from 1 to 9 micra. There are also small unmyelinated fibers ranging from 0.3 to 1.0 micron. The route of the myelinated fiber is from the vestibular division of the eighth nerve, through the connec- tive tissue to duabasement membrane of the crista which it penetrates to reach the sensory epithelium. Before reach- ing the sensory epithelium the nerve fibers lose their myelin and neurilemma sheaths. The naked axons divide 14 into a number of different size branches which ramify with— in the sensory epithelium. The larger nerve fibers give off many branches, each terminating in a nerve calyx around a type 1 hair cell. The smaller nerve fibers also divide into a number of branches which either form nerve calyxes or innervate type 11 hair cells. 2. The Utricle or "Little Skin Bag" (Figures A, B, C) The utricle is larger than the saccule and is the organ responsible for determining the position of the head in relation to the rest of the body. The utricle communicates with the sacculus by means of the utriculo-saccular duct and with the semicircular canals through five openings. The non—ampullated ends of the dorsal and caudal canals have a common opening into the utricle, but the ampullated end of each canal opens into the utricle independently. The lateral canal has two openings into the utricle. The utricle is lined with simple squamous or cuboidal epithelium resting on a basement membrane. There is a small mass of neuroepithelial cells and nerve endings located in the utricle. This is the macula or "little Sp0t." Bailey (1958) stated that the macula represents a local thickening of the membranous wall covering an area 15 of 3 mm. by 2 mm. and forming an elevation into the endo- lymphatic space. The epithelium is columnar and two types of cells, supportory and sensory, can be distinguished therein. The surface of the macula utricle is covered by a jellylike substance containing a number of calcareous bodies forming the otolithic membrane. The sensory and supporting cells are similar to those of the crista. As in the crista the basement membrane is penetrated by nerve fibers which lose their myelin sheaths shortly before entering the neuroepithelial regions. With any change in the position of the head there is a difference in pressure which acts on the otolithic membrane to stimulate the hair cells of the macula utricle. Guyton (1961) stated that the sensory axons wrap around the hair cells and bend the hair tufts to one side. In this position the axons transmit nervous impulses which inform the central nervous system of the relative position of the otoconia (calcareous bodies) in the gelatinous masses over the macula. The most important factor is the weight of the otoconia which compresses the hair tufts to produce a signal for the utricle. 16 3. The Saccule or "Small Sac" (Figures A, B, C) The saccule is more spherical in shape than the utricle and it is located in the central part of the membranous labyrinth. The saccule communicates with the utricle by the utriculosaccular duct and with the cochlea by the ductus reuniens. The saccular duct unites with the utricular duct to form the endolymphatic duct which extends through the vestibular aqueduct to the posterior part of the petrous temporal bone where it terminates in an enlargement the endolymphatic sac. Maximow and Bloom (1957) stated that the epithelium in both the macula saccule and the macula utricle is from 30 - 50 micra thick and it is made up of both sup- porting and sensory cells. The supporting cells are colum— nar in shape with broad bases in which the nuclei are located. These cells are connected to each other by ter- minal bars and the surfaces of the cells are provided with a cuticle. At the lateral periphery of the macula the sup- porting cells change from tall columnar to simple squamous epithelium similar to that lining most of the membranous labyrinth. The hair cells of the macula saccule intermingle with the supporting cells but are confined to the distal half 17 of the epithelium, while the supporting cells extend from the basement membrane to the surface of the epithelium. The hair cells are flask shaped with large rounded nuclei lying in their large bases. The free surfaces of the cells are provided with cuticular plates from which hairs pro- ject. The cuticular plates of the hair cells connect with those of the supporting cells. The spaces between the supporting cells and the hair cells are occupied by a semifluid substance. The hair cells terminate abruptly in the area where the supporting cells change from columnar to simple squamous. The connective tissue of the membranous labyrinth becomes thickened in the region of the macula and is firmly attadhed to the endosteum of the bone. The surface of the macula saccule is covered by a gelatinous otolithic mem- brane into which the hair tufts project. Each hair tuft is surrounded by endolymph. Beyond the hair tufts the oto- lithic substance contains a large number of crystalline bodies made of calcium carbonate, argonite, and a protein. These bodies are called otoconia or otoliths. The inner— vation of the macula saccule is similar to that of the macula utricle previously mentioned. 18 4. The Cupula The cupula is located in the ampulla of the semicir— cular canal and forms a cuplike structure over the crista. It consists of a network of undulating refracting fibers which form a complete network. Most authors have agreed that the cupula is a fixation artifact because it cannot be identified in fresh specimens. Bowen (1933) employed both light and darkfield microscopy in studying the cupula and he concluded that the cupula had neither cellular nor nuclear details. He further stated that the cupula was not a preformed structure which normally exists as a rounded cap above the crista. Instead, the structure described as the cupula is formed from thinly mucilagenous fluid presumably a secretion produced by glandular cells. Bowen in the same study stated that the cupula material is found in the living ear and occupies the endolymphatic space lying between the summit of the crista and the oppo- site ampullar wall. It is by the coagulation of this sub- stance that the cupula material is formed. 5. The Endolymphatic Duct (Figure A) According to Bast and Anson (1949) the endolymphatic duct extends from the junction of the saccular and the l9 utricular ducts through parts of the vestibule, through the vestibular aqueduct to end as an expanded portion of the endolymphatic sac which lies between the two layers of the dura. Bailey (1958) reported that the endolymphatic sac is located under the dura of the posterior surface of the temporal bone. Polyak §£_§l, (1946) related that the endo- lymphatic sac is located on the posterior face of the petrous pyramid under the dural lining of the posterior cranial fossa. The majority of evidences in the literature indicate that the endolymphatic sac lies under the dura. The proximal part of the duct is called the sinus. As the duct leaves the vestibule to pass through the vestibular aqueduct, it becomes narrow forming the isthmus of the duct. As the duct reaches the dural surface of the vesti- bular aqueduct it again becomes widened to form the endo- lymphatic sac. The first part of the duct has a rugose wall which gives it greater capacity. 6. Endolymph and Perilymph The labyrinth is bathed by two fluids designated as endolymph and perilymph. Perilymph is found in the spaces 0f the bony labyrinth and it therefore separates the bony labyrinth from the membranous labyrinth. Endolymph 20 is found in the membranous labyrinth. Smith §t_§1. (1954) explained that in guinea pigs the potassium con— centration of endolymph is 30 times greater than that of perilymph, but the sodium concentration of endolymph is only one-tenth that of perilymph. The chloride ion con- centration of endolymph is only 90% that of perilymph and cerebrospinal fluid. Perilymph and cerebrospinal fluid are indistinguishable with regards to potassium ion con- centration. All three fluids (perilymph, endolymph, and cerebrospinal fluid) are low in protein but perilymph might contain twice as much protein as either of the other two fluids. The origin of perilymph is said to be the cerebrospinal fuid via the subarachnoid space and scala tympani of the basal coil of the cochlea aqueduct. This origin is agreed by most authors. However, it is not very conclusive be— cause perilymph contains a greater concentration of protein than cerebrospinal fluid. Guild (1927) related that endolymph is formed by the stria vascularis, flows toward the basal coil of the coch- lear duct and into the endolymphatic sac via the intervening parts of the membranous labyrinth. The endolymph from the 21 cochlea, semicircular canals, and utricle flows into the sacculus and from here into the ductus endolymphaticus. From here it flows into the saccus endolymphaticus and leaves the membranous labyrinth by passing through the walls of the pars intermedia of the saccus into the small blood vessels of the region. The saccus endolymphaticus is the chief source of endolymphatic outflow. 7. The Vestibular Nerve and the Vestibular Ganglion The vestibular nerve is a division of the acoustic or eighth cranial nerve. Polyak t al, (1946) suggested that this branch is more than half the size of the total acoustic nerve because it contains very thick fibers. The fibers of the vestibular nerve originate from the bipolar ganglion cells located in the internal auditory meatus. Maximow and Bloom (1957) noted that both the vestibular nerve and the vestibular ganglion can be divided into inferior and superior parts. The peripheral branches of the bipolar ganglionic cells go to the five sensory areas. According to Maximow and Bloom, the superior vestibular ganglion sends out four branches which supply (1) the lateral ampulla; (2) the dorsal ampulla; (3) the utricular macula; (4) a small part of the saccular macula. From the inferior vestibular 22 ganglion three branches arise. The first supplies the larger part of the saccular macula; the second, the pos— terior ampulla; the third, the smallest, joins the fibers of the cochlear nerve. THE AUDITORY PORTION OF THE INNER EAR (Figures A, B, C) The auditory portion of the inner ear consists chiefly of the cochlea and the auditory portion of the eighth cranial nerve. The cochlea is shaped like a snail's shell, from which it derives its name. It is a bony canal which centers around a central core called the modiolus and ends blindly at the rounded tip called the cupula. According to Polyak §t_al, (1946) lengthwise the human cochlea measures approximately 35 mm.or almost one and one- half inches in length, and 2 mm. across. Both Maximow and Bloom (1957) and Bailey (1958) agreed that in man the cochlea makes two and one—half complete turns, but Polyak §£_§1, (1946) found that the human cochlea has two and three- fourths turns. He further reported that the number differs among other mammals: one and one—half coils in the hedge— hog, hamster, and porpoise; two in whale; two and one-half in cat and horse; three in hare; three and one-half in cattle; four in pig; up to five in guinea pig, but only a 23 half in the spiny anteater (even though the sense of hear— ing in this primitive mammal is very keen). Getty §§_§1, (1956) said that the cochlea of the dog makes three and one—fourth turns, and they also stated that in the dog the cochlea points "ventrodorsally." The osseous spiral lamina which wraps around the modiolus partially bisects the lumen of the spiral cochlear canal into two parts, the upper or scala vestibuli and the lower or scala tympani. The scala vestibuli makes connection with the vestibule, while the scala tympani makes connection with the middle ear through the round window. Both scalae com— municate with each other at the apex of the modiolus through a small opening the helicotrema. Getty et a1. (1956) found that in the dog the basal turn of the cochlea is about 4 mm. in diameter and lies close to the medial side of the vestibule. The total height of the cochlea is 7 mm. The base of the cochlea forms a part of the internal auditory meatus by means of which the fibers of the cochlear nerve enter the modiolus. The aggre_ gation of bipolar cell bodies located within the modiolus forms the spiral ganglion (Figures A, B, C). 24 FIGURE D clarity). Tectorial membrane Limbus spiralis Internal spiral sulcus External spiral sulcus Border cells Inner pillar cell Outer pillar cell Tunnel of Corti o (D ‘4 0‘ U‘ A ‘” 5o rd Nerve fiber passing through tunnel 0f Cortl Inner phalangeal cell H H r—a O . 0 Outer tunnel H N 0 Outer phalangeal cells H U) Cells of Hensen H 9 Cells of Claudius H U1 0 Cells of Boettcher H 0‘ Inner hair cell H \J 0 Outer hair cell H CO Branch of cochlear nerve Spiral vessel NH OKO Basilar membrane . U o I: I - announ- II I I II I... .Q I .I ‘ ., L . \ ~\ I I II I . .\ II/.’/H . ..... e , / ' lilo num‘fi I. , ...o a o I I ... l n I. In. I I . , . ' I UOIIOOIIIII I O Ila-DI . I'IO'OII 0' "I JI nIlIlI s ‘0 .1 O 0.00 I I. In. . .. On I I a. .00.: I I0 I .00.. I". me. I K r. f r I‘ 0’ . . . . . o .0 O IIIIOI III a I I: s «'1‘. I 0 VII- . u. I . I , o L I I. I On I ' I‘n \ n It. I 0 II . l "I II l‘c‘ui ‘t CID. I II. II ’1. I. In! v . no ‘I u a I o I nun-HI”... - . a ...-II "ac-{\Hto’n aw o \o..00”'-\Ia noun-oo-IIIIIJGII - I. -I I 0.1.. .I..a no. ....... . .. 3% {.033 )umw ...... 6.. -..®..................,.a....... ..... . - .. .. . .... .o 1.. as .. 9.1 Q ............. I In '0 0. II n. . .o III“ II e "QI'I‘I‘I‘. .- ....... ”I‘ll-II: II... II. \ ..- o 0"! II, II I a I‘o ‘ II lav: II.- nlIoo lllllllllll I}:’ n I l I. I 00.0 ‘ ‘ Oil - I I o n a . O l I I]. Iqui’I "L‘D/ .- D, o/ I I! a I II a u I u I . o u o u n I. I I O I 0’. o u”;¢¢OIIIo 0., I... an“: I. .- I u OOO‘o’nII 0- II I I! 0.. o I I III I. . I . you. .- .. .au OoolI. o alt-o I It I II I. In... ’09 I 00- f. I on: .- I .o o. n In I nu on, o- .o o {a I o a \ .0 \ oo o I .- no a o . .- 9. on o. I on a I- . o I a o I w I . ......../... >rt1 or “om a ded 0' 0R 0’..." ....@.v.....l...,mw.., I I I'I‘ 0‘ IIIII .- III. . III. III “a I assault-IIIIII. . ....... l...../....® u... I H... .I...I .. 0@ . ..n...u\@..\m@d\\. .. \\ I I I II III. II‘I‘III III-I IIIIOIIIII\\ IIIIIIIIIIIII I I It‘ll It". I‘ II I‘ \I II 0‘ I II . II ’ . ‘ |‘:'|I“ III I ..... II IIII I I I XIII-III III-IID‘IIII II, I.‘ I I ‘I II III. II II‘II III I x U I ’: .......... 0‘ I I . '0 I D I ‘ The The The The The The The The The The U‘fll th'thaO BHWuJ—hb‘ The 26 cochlea is composed of many parts as listed below: osseous spiral lamina scala media or cochlea duct vestibular or Reissner's membrane basilar membrane spiral ligament stria vascularis modiolus organ of Corti organ of Corti (Figure D) is made up of the following: Tectorial membrane Limbus spiralis Internal spiral sulcus External spiral sulcus Border cells Inner and outer pillar cells The tunnel of Corti Inner phalangeal cells Outer phalangeal cells or cells of Deiters Cells of Hensen Cells of Claudius Cells of Boettcher Sensory hair cells cochlear nerve and spiral ganglion 27 l. The Osseous or Bony Spiral Lamina The osseous spiral lamina described by Polyak et_al. (1946) is a shelf of bone arising from the inner or modiolar wall of each coil of the cochlea along with the membranous tissue which divides the cochlear channel into two com- partments, an upper scala vestibuli and a lower scala tym— pani. The width of the bony lamina varies from the base to the apex of the cochlea. The outer wall of the osseous spiral lamina contains the limbus spiralis. 2. The Scale Media or Cochlear Duct According to Bast and Anson (1949) the cochlear duct is primarily an epithelial tube of ectodermal origin. The duct is triangular in cross section and its walls are formed by various structures. Its upper wall is formed by the ves- tibular membrane, the outer wall is formed by the spiral ligament, and the lower or tympanic wall is formed by the outer part of the osseous spiral lamina plus all of the membranous spiral lamina. The cochlear duct communicates With the sacculus through the ductus reuniens. The cochlear duct contains endolymph. 28 3. The Vestibular or Reissner's Membrane Most authors agree that the vestibular membrane is made up of a single layer of flat epithalial cells and fine fibers which stretch in an oblique manner from the vestibular surface of the osseous spiral lamina slightly inwards from the point where the tectorial membrane is attached to the outer wall of the cochlear channel. This membrane forms one of the walls of the cochlear duct, and separates the scala vestibuli from the cochlear duct. Bailey (1958) found that the non—vascular vestibular membrane consists of a thin central lamina of connective tissue covered on either side by simple squamous epithelium. 4. The Basilar Membrane (Figure D) This membrane lies between the scala media, scala tym— pani, and spiral ligament. According to Bailey (1958) this membrane is made up of straight unbranched fibers, auditory strings, embedded in a homogeneous ground substance. It is divided into inner zona arcuata (or zona tecta) and an outer zona pectinata. The basilar membrane has both a vestibular covering layer and a tympanic covering layer. The vestibular layer is thinner and is made up of a homogeneous substance With few connective tissue cells. The tympanic covering 29 layer is thicker and is made up of cellular connective tissue. Directly under the tunnel of Corti the basilar membrane contains blood capillaries, the most prominent of which is the spirally shaped vas spirale. The width of the basilar membrane varies with the different coils of the cochlea. The width of the membrane is greatest at the apex, gradually diminishing toward the base and narrowest in the proximal end of the basal coil. Polyak e§_§l, (1946) reported that the basilar membrane is attached inwardly to the tympanic lip of the osseous spiral lamina and outwardly to the inner crest of the spiral ligament. He reported ZLCDO fibers in this membrane. They are named strings or cords and parallel each other. The upper or vestibular side of the basilar membrane (which faces the cochlear duct) contains the organ of Corti named after its discoverer. This is the specific receptor for hearing. 5. The Spiral Ligament (Figure D) The outer wall of the cochlear duct is formed by the spiral ligament, a triangular shaped thickening of the periosteum. The outer wall of the spiral ligament Wthh is closest to the bone is made up of dense fibrous connective 30 tissue, whereas the part closer to the stria vascularis is more loosely arranged. According to Bailey (1958) the crest of the spiral ligament forms the crista basilaris which serves for the attachment of the membranous spiral lamina. It contains dense converging fibers and relatively few cells. A small ridge, the spiral prominence, which contains blood vessels is a part of the spiral ligament and this ridge is separated from the organ of Corti by a small depression, the external spiral sulcus. The fibers in the spiral ligament cross in all directions, but most of them converge at the crest or inner margin of the spiral liga— ment which is a tough homogeneous tissue and forms the attachment for the basilar membrane. 6. The Stria Vascularis The stria vascularis is that part of the spiral ligament which is located between the spiral prominence and the vestibular membrane. In this region the epithelium is thick and pseudostratified. There is no basement membrane 9 between the spiral ligament proper and the stria vascularis. The subepithelial connective tissue of the stria is richly supplied with blood vessels, some of which send loop into the epithelium causing it to appear very vascular. According 31 to Lurie and Nachlas (1951) Corti first reported that the stria vascularis was connected with the secretion of endo— lymph in 1854. Lurie in the same study also reported that Deiters in 1860, and Hensen in 1863 verified the findings of Corti. Even today most investigators still uphold this finding. 7. The Modiolus (Figure C) The modiolus is a cone shaped pillar of spongy bone which forms the core of the cochlea. The base of this bony structure forms the bottom of the internal acoustic meatus. A number of blood vessels and nerve fibers of the cochlear nerve pass through the openings in the modiolus. 8. The Organ of Corti (Figure D) The organ of Corti is the end organ for auditory stimu- lation and extends throughout the length of the cochlea. This structure is made up of many types of cells and it rests on the basement membrane. Buchanan (1957) noted that in cross section there is a triangular tunnel running throughout the cochlea. This is the tunnel of Corti. On both sides of the tunnel and contributing to its formation are the inner and outer pillars of Corti. A single row of 32 hair cells is located on the inner side of the inner rod and three or four rows of these same types of cells are located on the outer side of the outer rod. Each hair cell is surmounted by 20 hairlike processes. The inner and outer hair cells are supported by rows of columnar cells. Medial to the organ of Corti there is a space designated as the internal spiral sulcus. The tectorial membrane overhangs this space and the organ of Corti. Buchanan believed that the processes of the hair cells are embedded in the under surface of the tectorial membrane. The tectorial membrane is said to have a dampening effect on the hair cells. a. Tectorial Membrane (Figure D) Polyak t al, (1946) related that the tectorial membrane extends the complete length of the cochlear duct and this membrane is made up of many fine fibers. The inner fibers are attached to the vestibular lip and the other side of this organ protrudes into the cochlear space. Bailey (1958) observed that the tectorial or Corti's membrane, appears as a continuation of the columnar cells of the limbus. Towards the edge of the vestibular lip there is a thickening of the cuticular formation to form a striated gelatinous structure overhanging the internal spiral sulcus and extending to the 33 cells of Hensen. The upper surface has a more convex shape than the lower. The tectorial membrane is easily distorted by fixing agents. Quite often it is shrunken and separated from the processes of the hairs in fixed preparations. In the living conditions the hair cells are believed to make contact with the tectorial membrane and movements of the membrane result in stimulation of the hair cells. Polyak _£_§l, (1946) found that the fibers of the tectorial mem- brane extend in a direction radial to the axis of the cochlea with marked deviations toward the lower surface. b. The Limbus Spiralis (Figure D) The limbus spiralis is located on the outer wall of the osseous spiral lamina. The limbus is very cellular and is grooved longitudinally by a furrow, the spiral sulcus, which separates it into a lower or tympanic lip and an upper or vestibular lip. The tympanic or lower lip is also called the perforata habenula and it possesses a small opening through which the cochlear nerve passes to the organ of Corti. This lip extends more laterally into the cochlear channel than does the vestibular lip. The tympanic lip is thinner near the extremity and instead of terminating with a free margin it ends as the basilar membrane. The 34 vestibular lip extends into the tectorial membrane. Bailey (1958) stated that the vestibular membrane is attached to the upper surface of the limbus. Lateral to this point of attachment the limbus is covered by columnar epithelium with a cuticular border. On the surface, the limbus has many ridges which overhang the surface of the vestibular lip forming processes called the auditory teeth of Huschke. Poltz and Perlman (1955) showed that these teeth are made up of condensed fibers which are deeply stained by the Hotchkiss method. (According to Pearse (1960) the Hotchkiss method is a type of periodic acid- Schiff reaction (PAS). Periodic acid is an oxidizing agent and according to Pearsevfim first described for histo- lOgical use by McManus in 1946 for the demonstration of mucin but later by Lillie in 1947 and Hotchkiss in 1948 elaborated the method into a histochemical one which can be used to demonstrate a variety of polysaccharide sub- stances in the tissues. This method will stain any chami- cal in the tissue which has a potential aldehyde next to a carboxyl group. The method gives a reaction for poly- saccharides, hyaluronic acid, mucoproteins, unsaturated lipids and phospholipids.) 35 c. Internal Spiral Sulcus (Figure D) This is a groove which is partially enclosed by the vestibular and tympanic lips of the limbus spiralis. The tectorial membrane hangs over this groove. d. The External Spiral Sulcus (Figure D) The external spiral sulcus is a depression located between the organ of Corti and the spiral prominence. Bailey (1958) stated that this depression is covered by cuboidal epithelial cells. e. The Border Cells (Figure D) These are slender columnar elements resting on the tympanic lip of the limbus spiralis and exist as a single row along the inner side of the inner hair cells. f. Inner and Outer Pillar Cells (Figure D) The inner and outer pillar cells are the most conspic— uous of the supporting cells. Polyak _£_§l, (1946) reported that these cells are called pillars because of their straight smooth appearance, their stiff thick tonofibrils, and their arrangement which suggests supporting functions. These two types of cells converge at their upper ends. The pillar membrane. Cells have broad bases which rest on the basement 36 Bailey (1958) and Maximow and Bloom (1957) noted that the nuclei of the pillar cells are located in the broad bases of the cells. Bailey further suggested that these cells have elongated bodies representing a condensation of rigid deeply stained tonofibrils. The thickened part of the pillar away from the base is called the head and its sur— face contains a cuticular plate to which the tonofibrils are attached. According to Bailey (1958) the outer pillar cells are larger and fewer in number than the inner pillar cells. He also estimated that the number of pillar cells in the human cochlea is 3,800 outer and 5,600 inner. g. The Tunnel of Corti (Figure D) The inner and outer pillars enclose a space, the inner tunnel or Corti's tunnel. This tunnel is crossed by deli- cate nerve fibers. h. The Inner Phalangeal Cells (Figure D) According to Bailey (1958) and Maximow and Bloom (1957) the inner phalangeal cells are arranged as a single row of columnar cells on the inner surface of the inner pillars. These cells have broad bases which rest on the basilar mem— brane. The nuclei of the cells are located in the broad 37 bases. The surfaces of the cells contain tonofibrils. These cells are the supporting cells for the inner hair cells. A rigid bundle of tonofibrils passes through the cytoplasm of the cells. i. The Outer Phalangeal Cells or Cells of Deiters (Figure D) The outer phalangeal cells are the supporting cells for the outer hair cells, one for each hair cell. Bailey (1958) and Maximow and Bloom (1957) noted that like the hair cells the outer phalangeal cells vary in number in the different coils of the cochlea. In the basal coil there are three rows of cells, in the middle coil there are four, and in the apical coil there are five. The outer phalangeal cells are also columnar shaped with their broad bases resting on the basilar membrane. The nuclei are in the bases of the cells and the surfaces of the cells con- tain tonofibrils. At the level of the bases of the hair cells each phalangeal cell bears a facet which receives the base of the hair cell. The phalangeal cells support the hair cells. j. Cells of Hensen (Figure D) These are tall columnar cells arranged laterally to the 38 outer phalangeal cells and are arranged in many rows on the basilar membrane. Toward the periphery the cells decrease in height and they pass into the cells of Claudius. k. Cells of Claudius (Figure D) These are cuboidal cells with clear cytoplasm which are located on the lower surface of the external spiral sulcus. 1. Cells of Boettcher (Figure D) These are small clumps of cells located in some areas of the basal coil of the cochlea. These cells are deeply staining with finely granular cytoplasm and located between the basilar membrane and the cells of Claudius. m. Sensory Hair Cells of the Organ of Corti (Figure D) The sensory hair cells of the organ of Corti are classi- fied as inner and outer hair cells. According to Engstrom and Wersall (1953) these cells are designated as hair cells because their surfaces have a large number of filamentous processes. These authors also found that these hair cells occur in different numbers and that they are differently arranged in different animals. In man there are 100 hairs arranged to form the letter M on the surface of each hair cell. The guinea pig has a smaller number of hair cells 39 and these are arranged in a U formation. 9. The Cochlear Nerve and the Spiral Ganglion The organ of Corti is innervated by the cochlear divi- sion of the eighth cranial nerve. This division of the nerve enters the modiolus from the internal auditory meatus after which it divides into many branches from which fibers radiate to the osseous spiral lamina in which the spiral ganglion lies. According to Bailey (1958) the cells of the spiral ganglion maintain their embryonic bipolar condition throughout life. Their central processes pass through the modiolus, then through the internal auditory meatus to their terminal nuclei in the medulla. Their peripheral processes also become myelinated and pass outwards in bundles in the osseous spiral lamina. From these are given off branches which enter the tympanic lip of the limbus, where they lose their myelin and pass through the foramina nervosa (minute apertures in the tympanic lip) to their terminations in the organ of Corti. In the latter, the fibers run in three bun- dles parallel to the inner tunnel. One bundle lies just inside the inner pillar beneath the row of inner hair cells. A second bundle runs in the tunnel to the outer side of the inner pillar. The third bundle crosses the inner tunnel 4O (tunnel fibers) and turns at right angles to run between the outer phalangeal cells. Branches from all these nerve bundles end around the bases of the hair cells. Polyak §t_§1, (1946) noted that of the two divisions of the eighth cranial nerve the cochlear branch is less than half the total size of the entire nerve while the vestibular branch is larger and occupies more than half the size of the nerve. The cochlear nerve has a larger number of smal— ler fibers while the vestibular nerve has a smaller number of larger size fibers. The total number of fibers in the eighth cranial nerve (as counted by Rasmussen) and as cited by Polyak §E_al, (1946) is rather small, amounting to only from 38,000 to 64,000, or on the average 49,500. In the vestibular division the number of fibers varies from 14,000 to 24,000 being on the average 18,500; in the cochlear division there are 24,000 to 40,000 fibers, or on the average 31,000. In agreement with the smaller size of the fibers of the cochlear nerve in comparison with those of the vestibular nerve, the bipolar ganglionic cells of the sPiral ganglion are much smaller than those of the vesti- bular ganglion. MATERIALS AND METHODS The material for this study consisted of 14 ears from seven normal adult dogs obtained from the Departments of Physiology and Surgery and Medicine of the Michigan State University. Each dog was anesthesized with Nembutal, one of the carotid arteries was cannulated and the head was perfused with .85% saline followed by 10% buffered formalin. In five of the dogs the right and left temporal bones were removed immediately after the animals were killed and these bones were placed in 10% buffered formalin for 14 days. In the other two dogs the temporal bones were left attached to the brain and care was taken to remove the temporal bone with the brain in order to obtain an intact eighth nerve. These brains and temporal bones were fixed in 10% buffered formalin for a period of eight weeks to ensure the proper fixation of the brain tissue which requires a longer fixa- tion period than bone. After formalin fixation, each specimen was washed thoroughly under running tap water for a period of 24 hours after Which it was placed in a decalcifying medium of either 41 42 commercial Decal,* sodium acetate formic acid, or three percent hydrochloric acid for varying periods of time. The time required for the bones to be completely decalci— fied in commercial Decal was from four to six days with two to three changes of the decalcifying solution. Decalcifi— cation was very rapid with three percent hydrochloric acid, and the required time for decalcification in this medium was from three to four days. The specimens which were de— calcified in sodium acetate formic acid solution required the longest time for complete decalcification. Complete decalcification in this medium required a period of approxi- mately 10 days with changes of the decalcifying medium every two days. The only specimens which were decalcified in sodium acetate formic acid solution were those in which the temporal bones were left attached to the brain. At the end of the decalcifying period each specimen was thoroughly washed under running tap water for 48 hours. After washing, the specimens were dehydrated in a series of graded ethyl alcohol, cleared in xylene, and embedded in Tissuemat** under vacuum and sections were cut at 12 micra. *Scientific Products, Division of American Hospital Sup- Ply Corporation, Evanston, Illinois. **Fisher Scientific Company, Pittsburgh, Pennsylvania. 43 The temporal bone which contained the ear was oriented in the melted Tissuemat in such a way that horizontal sections were cut passing through the external auditory meatus which was used as a guide for obtaining horizontal sections of the inner ear (Figure A). The specimens in which the temporal bones were left attached to the brain were oriented in a different manner. Here the specimens were so oriented for sectioning that cross sections were made of the brain and the temporal bone attached to it. The histological sections of the inner ear obtained with this orientation of the specimen were not as good for studying the histology of the inner ear but they gave good details of the relationship of the eighth nerve to the brain and to the parts of the inner ear. A number of sections were selected from each specimen and these were stained with either Harris' hematoxylin and eosin, Weigert's Van Gieson's connective tissue stain, or by the Crossmon's (1937) modification of the Mallory's tri- chrome stain. The most satisfactory results were obtained with the Crossmon's modification of the Mallory's Trichrome stain. By the use of this stain it was possible to obtain a better picture of the histology of the inner ear of the 44 dog. With the Weigert's Van Gieson's connective tissue stain it was difficult to obtain the cellular details of the different structures probably due to the effects of decalcification. It was good for differentiating between collagenous and elastic connective tissue in the different structures of the auditory portion of the inner ear. Harris' hematoxylin was the next most effective stain. Measurements of the different parts of the inner ear were made with a calibrated ocular micrometer. The meas- urements listed represent the exact average of several different observations. RESULTS THE VESTIBULAR PORTION OF THE INNER EAR OF THE DOG 1. The Semicircular Canals (Plates I, II, V, VI) It is very difficult to histologically obtain all three canals in the same slide because of their gross relation— ship. Plate I shows a horizontal section through the mem— branous labyrinth in which the dorsal and caudal semicircular canals are seen in relationship to the utricle. Because of the structural similarity of the canals, only the dorsal semicircular canal is described (Plate II). The ampulla of the canal is of greatest functional importance because it contains the crista. The dorsal semicircular canal is enclosed by bone in a space which contains perilymph in the living animal. The shape of the membranous labyrinth is similar to that of the bony canal in which it lies. The greater portion of the membranous semicircular canal is the endolymphatic space. The remainder of the canal is occupied by the crista ampul- laris which is a rounded prominence extending for some distance into the lumen of the canal. This part of the canal also contains endolymph. The base of the crista, which 45 46 contains the fibers of the vestibular nerve is broad while the part which protrudes into the lumen of the canal is narrower and somewhat conical (Plates II, III, IV). The conically shaped crista is highest in the middle and decreases in height toward the periphery (Plates II, III, IV). The surface of the crista which faces the lumen of the canal is covered by pseudostratified columnar epi— thelial cells resting on a basement membrane (Plates II, III, IV). The epithelium is covered by a thin cuticle formed by the combined cuticles on the surfaces of the hair cells and the supporting cells. Numerous hairlike projec- tions are seen on the free surface of the crista. These hairs extend all the way from the surface of the hair cells to the cupula. Toward the lateral periphery of the crista the pseudostratified columnar epithelium becomes continuous with the simple squamous epithelium lining the greater por- tion of the semicircular canal (Plates III, IV). The sensory epithelium of the crista is made up of two different types of cells described as hair cells and support- ing cells. The hair cells are more intensely stained than the supporting cells. The hair cells are found in the outer region of the sensory epithelium and were not seen to extend 47 to the basement membrane. It was not possible with light microscopy to observe the two types of hair cells described by Wersall (1956). The hair cells observed in this study are flask shaped (Plates III, IV). The large rounded nuclei are located in the broad bases of the cells. The free sur- face of the cell is covered by a rounded citicular plate through which one long tapering hair passes. Each hair has an inner darkly stained portion and a peripheral lightly stained portion. These hairs extend from the surface of the epithelium to penetrate the cupula. The supporting cells of the crista are slender columnar cells which extend from the basement membrane to the cuti- cular surface of the crista. The cytoplasm of the cell is poorly stained but the basally located nucleus is very in— tensely stained. The surface of the supporting cells is covered with a rounded cuticle resembling that of the hair cells but devoid of hairlike projections. Toward the lateral periphery of the crista the hair cells are absent and the Supporting cells show a gradual transition from columnar to Squamous epithelium which lines the remainder of the mem- branous labyrinth. The stroma of the crista is made up of fairly loose 48 connective tissue which contains a number of spindle shaped cells and collagenous connective tissue fibers. Numerous nerve fibers from the vestibular division of the eighth nerve travel through the connective tissue of the crista to innervate the hair cells in the sensory epithelium. Several small blood vessels are seen in the connective tis- sue (Plates II, III, IV). 2. The Utricle (Plates I, VI, VII) The utricle is closely related to the semicircular canals and the sacculus. The greater portion of the utri- cle is lined by simple squamous epithelial cells except in the region of the macula. The macula of the utricle is a local thickening of the membranous wall which extends into the endolymphatic space. The local thickening is not as great in height as the crista of the semicircular canal but it is greater in length. As in the case of the semicircular canals, the outer portion of the macula is covered by a layer of pseudo- stratified columnar cells which rest on a distinct basement membrane. The same two types of cells, hair cells and Supporting cells in the crista are found in the macula utricle. The hair cells are flask shaped with rounded 49 bases containing the nuclei. These hair cells are located in the outer portion of the sensory epithelium while the supporting cells extend all the way to the basement mem— brane. The surface of each hair cell contains a thin rounded cuticle through which a thin tapering hair pro— trudes to the otolith membrane which lies on the free sur— face of the macula. The hairs from the hair cells of the macula are smaller than those which protrude from the hair cells of the crista. However, the hairs found in the macula are structurally similar to those in the crista. The hairs from the hair cells project into the otolith membrane which appears acellular and consists of a network of very small densely staining fibers in which are sus- pended a number of iridescent bodies. The supporting cells of the macula are morphologically similar to those of the crista. The midportion of the macula utricle is the high— est which gradually tapers to the periphery. At the peri- phery of the macula the pseudostratified columnar epithelium changes from columnar to simple squamous which lines the greater portion of the membranous labyrinth. The basement membrane under the pseudostratified colum— nar epithelium is more distinct in the macula than in the 50 crista. The macula is mostly made up of connective tissue containing predominantly branched collagenous fibers in which are scattered a number of spindle shaped connective tissue cells. The branch of the vestibular nerve which sup— plies the macula utricle also travels through the connective tissue to innervate the hair cells of the sensory epithelium. A number of small blood vessels are seen in the connective tissue of the macula utricle (Plates VI, VII). 3. The Sacculus (Plate VI) The smaller sacculus is more closely related to the cochlea than the utricle. As in the case of the utricle the sacculus contains a sensory area, the macula saccule. The hairs of the macula saccule are about the same length as those of the macula utricle but they are not as long as those of the crista. The morphology of all the hairs is the same as that previously mentioned for the crista. The hair tufts of the macula saccule project into the otolith mem— brane which lies directly over the epithelium of the macula. The otolith membrane contains a number of lightly stained crystalline bodies. Specific chemical tests were not car— ried out in order to determine the specific chemical 51 composition of these bodies, but according to Maximow and Bloom (1957) these are a mixture of calcium carbonate and a protein. 4. The Cupula (Plates II, III, IV) An acellular structure, the cupula, has been observed in this study. The cupula is made up of a network of fibers and it is located directly over the sensory epithelium of the cristae of the semicircular canals and is not found beyond this region. The hairs from the hair cells of the epithelium extend all the way to the cupula and make con- tact with it. The structure of the cupula appears similar to that of the otolith membrane except for the absence of the large number of crystalline bodies in the cupula. The shape of the cupula is similar to the underlying crista. Due to the fact that fixed specimens were studied by light microscopy it was not possible to determine whether or not the cupula is a fixation artifact. 5. The Vestibular Nerve and the Vestibular Ganglion (Plate VIII) The vestibular nerve is a branch of the eighth cranial nerve and as seen in Plate VIII enters the medulla at the level of the ventral border of the restiform body. The fibers 52 of the vestibular nerve originate from the bipolar cells of the vestibular ganglion which is located in the internal auditory meatus. The cell bodies of the vestibular gang- lion are much larger than those of the spiral ganglion (Plate XI). The peripheral branches of the bipolar ganglionic cells innervate the five sensory areas of the vestibular mechanism in Plates II, III, IV, V, VII. These fibers travel through the connective tissue of the five neuroepithelial regions and terminate in their sensory cells. It was not possible in this study to show in detail the innervation of the sensory hair cells. THE AUDITORY PORTION OF THE INNER EAR 1. The Osseous Spiral Lamina (Plate X) The osseous spiral lamina is seen as a shelf of bone extending from the modiolus to the lamina spiralis. This bony lamina is thickest in the basal coil of the cochlea where it is 96 micra wide at its base. It decreases in thickness to 65 micra in the second coil, 52 micra in the third coil, and to a very small vestige in the last one- fourth coil. 53 The fibers of the cochlear nerve extend from the spiral ganglion in the modiolus to enter the bony lamina for in- nervation of the organ of Corti. The largest number of nerve fibers are seen in the osseous spiral lamina of the basal coil of the cochlea. The number of nerve fibers seems to decrease from the basal to the apical coil. This apparent decrease in the number of nerve fibers corresponds to the decrease in the thickness of the osseous spiral lamina. The fact that the organ of Corti in the last one and one- fourth coils of the cochlea is much larger in comparison with that of the basal coil should require a greater number of nerve fibers to innervate it. Thus there may not be a real decrease in the number of fibers but these may become more compact. The part of the osseous spiral lamina which is attached to the limbus is thickest and tapers progressively toward the point where the nerve fibers enter the organ of Corti. The osseous spiral lamina has two faces. The limbus SPiralis is on the upper or vestibular face, and the lower or tympanic face is covered by a single row of cells. 2. The Scala Media or Cochlear Duct (Plate XII) The scala media is triangular in shape. Its upper wall 54 is formed by the vestibular membrane, the outer wall by the spiral ligament, and the lower by the osseous spiral lamina. The organ of Corti is located in this duct. The stria vas— cularis of the spiral ligament secretes endolymph into this duct. 3. The Vestibular or Reissner's Membrane (Plate XII) In the dog this membrane extends in an oblique manner from the upper tip of the stria vascularis of the spiral ligament to the upper border of the limbus spiralis. The vestibular membrane has two surfaces, one exposed to the scala vestibuli and one exposed to the cochlear duct. Each surface layer is composed of simple squamous epithelium which rests on a common base of extremely thin connective tissue located between the two surfaces. Both the Weigert‘s Van Gieson's connective tissue stain and the Crossmon's modification of the Mallory's Trichrome stain failed to reveal the exact nature of the homogeneous appearing con— nective tissue. The average thickness of the vestibular membrane is 11 micra. The average length from the stria vascularis to the limbus spiralis is approximately 650 micra. In agreement with Bailey (1958) the vestibular membrane is non-vascular. 55 As described above, this membrane forms the upper wall of the cochlear duct, and separates the scala vestibuli from the cochlear duct. 4. The Basilar Membrane (Plate XII, Figure D) The basilar membrane stretches from the end of the tympanic lip of the limbus to the crest of the spiral liga- ment. It has a vestibular covering layer with a small number of connective tissue cells. There is also a lower or tympanic lip which is thicker and consists of rounded and spindle shaped connective tissue cells and few very fine connective tissue fibers. In agreement with previous in- vestigators, both the zona arcuata and the zona pectinata could be established in this study. The zona arcuata of the basilar membrane extends from the tympanic lip of the limbus spiralis to the outer pillar of the inner tunnel of Corti (Figure D). A small blood vessel (the spiral vessel) is seen in the connective tissue directly under the inner tunnel. The zona pectinata is seen as that part of the basilar membrane which extends from the outer pillar to the spiral ligament. The basilar membrane is made up of straight unbranched fibers which parallel each other. The average thickness of 56 the basilar membrane exclusive of the covering layers is approximately 3.3 micra except in the region directly under the outer phalangeal cells where it increases to 4.4 micra. The average thickness of this membrane including the tympanic lip and vestibular covering layer is 8 micra and in the region of the outer phalangeal cells it is 15 micra. The basilar membrane is shortest in the basal coil where it measures 286 micra and longest in the apical coil where it measures 500 micra. The average length of the second coil is 390 micra, and that of the third coil is approxi- mately 497 micra. 5. The Spiral Ligament (Plate XII) The spiral ligament is formed by the thickening of the periosteum of the outer wall of the cochlear duct. It is triangular in shape with the base of the triangle towards the bony wall of the cochlear duct and the apex attached to the basilar membrane. The spiral ligament is widest and consists of denser fibers in the basal coil of the cochlea as compared with the narrowness and the loose arrangement 0f the fibers of this ligament in the apical coil. The average measurements (measuring from the periosteum to the crest) for the different coils are: first coil, 315 micra; 57 second coil, 156 micra; third coil, 130 micra and the last one—fourth coil, 78 micra. The spiral ligament is made up of a large number of irregularly arranged collagenous fibers converging upon a central point called the crest. At the crest the fibers are very compact and form the point for attachment of the basilar membrane. There are a number of rounded to stellate shaped cells among the fibers of the ligament. The greatest concentration of these cells is in the part of the ligament closest to the bony wall, while their number decreases from the periosteum toward the crest. Between the external spiral sulcus and the stria vas- cularis, the spiral ligament gives rise to a small ridge, the Spiral prominence, which contains blood capillaries and veins. Long slender thin walled blood vessels from the spiral prominence travel medially toward the part of the ligament attached to the bone. Thus, the spiral ligament is richly supplied with blood. The cells and fibers of the spiral prominence are intensely stained and the free surface of this structure is covered by a single row of cuboidal epithelial cells. 58 6. The Stria Vascularis (Plate XII) The stria vascularis is seen as an intensely staining structure forming the medial portion of the spiral ligament and extending from the spiral prominence to the point of attachment of the vestibular membrane to the spiral liga- ment. It is made up of a layer of darkly stained pseudo- stratified columnar epithelium cells which does not rest on a basement membrane. This layer merges into the less in— tensely stained cells and fibers of the remainder of the spiral ligament. The narrowest portion of the stria vascularis is at the point at which it is directly connected to the spiral prominence. A number of thin walled blood vessels are located in the stria vascularis, particularly near the sur- face which faces the cochlear duct. These blood vessels penetrate into the remainder of the spiral ligament. The stria vascularis forms part of the epithelial lining of the cochlear duct. The average width through the mid portion of the stria vascularis is reduced from the basal to the apical coil of the cochlea but its length appears to remain the same throughout the different coils of the cochlea. The average width of the mid portion of 59 the stria vascularis in the basal coil is 32.5 micra, in the second coil it is 20.5 micra, while in the last one- fourth coil it is reduced to 19.5 micra. 7. The Modiolus (Plate XIII) The modiolus is seen as the central bony axis around which the cochlea winds. It consists of spongy bone which is widest in the basal coil and in the apical coil only a small vestige of the bony structure remains. Cochlear nerve fibers travel through the modiolus on their way to innervate the organ of Corti. The fibers of the cochlear nerve enter the modiolus at the basal coil and travel in this structure to all the coils of the cochlea. From the centrally located modiolus nerve fibers are given off which travel in the peripherally located osseous spiral lamina to innervate the sensory hair cells of the organ of Corti. The SPiral ganglion is located in the highly vascularized modiolus. 8. The Organ of Corti (Plates XII, XIV; Figure D) The organ of Corti is made up of a number of different structures described below. It is smallest in the basal coil and largest in the apical coil in conformity with the 60 increase in the size of both the basilar and the tectorial membranes. The length of the organ of Corti measured from the crest of the spiral ligament to the tympanic lip of the modiolus for each coil is listed below. The thickness of the organ through the mid portion is also listed. Coil of Length of Thickness of Cochlea Organ of Corti Organ of Corti l 130 micra 19.5 micra 2 195 micra 45.5 micra 3 208 micra 45.5 micra 3 1/4 195 micra 45.0 micra a. The Tectorial Membrane (Plates XII, XIV; Figure D) The tectorial membrane arises from the vestibular lip of the limbus spiralis. Unlike the limbus spiralis, the tectorial membrane is acellular and consists of a number of wavy fibers which appear to be collagenous. The tectorial membrane overhangs the internal spiral sulcus and in the aPical coil it stretches beyond the mid portion of the organ of Corti and appears to be touching the projections of the hair cells. The greatest size of the tectorial membrane is in the third coil of the cochlea. This is in agreement with the 61 largest size of the organ of Corti in the same coil. The vestibular lip, to which the tectorial membrane is attached, is reduced in diameter from the basal to the apical coil of the cochlea. The average measurements of the tectorial membrane in the different coils of the cochlea follow. Coil Length of Width of Membrane Membrane l 117 micra 12 micra 2 143 micra l3 micra 3 182 micra 15 micra 3 1/4 208 micra l7 micra b. The Limbus Spiralis (Plates XII, Figure D) The limbus spiralis is seen as a collagenous connective tissue structure located in the inner corner of the cochlear duct and arises from the periosteum of the vestibular surface of the osseous spiral lamina. It terminates in an upper or vestibular lip and a lower or tympanic lip (Plate XII). The vestibular lip does not extend as far inwards as does the tYmpanic lip. The tectorial membrane is located at the end of the vestibular lip and the basilar membrane of the organ of Corti is connected to the tympanic lip (Plate XII)- In the upper part of the limbus the fibers form a network 62 arrangement but toward the tympanic lip the fibers run more parallel to each other. Toward the surface of the limbus there is a layer of deeply staining pseudostratified colum- nar epithelial cells with darkly stained nuclei. The limbus is richly supplied with small blood vessels. The length and width of the limbus spiralis decrease from the base to the apex of the cochlea. Coil of Length of Width of Cochlea Limbus Limbus l 260 micra 97.5 micra 2 247 micra 71.5 micra 3 227 micra 58.5 micra 3 1/4 130 micra 26.0 micra The cochlear nerve passes through a small opening in the tympanic lip of the limbus on the way to innervate the Organ of Corti. In this region the nerve is reduced to a few fibers and this occurs in all coils. c. Internal Spiral Sulcus (Plate XII, Figure D) The internal spiral sulcus is a groove which is par- tially enclosed by the vestibular and tympanic lips of the limbus spiralis, and the tectorial membrane overhangs this 63 groove. In the basal coil of the cochlea the internal spiral sulcus is wider in diameter and circular in shape, while in the apical coil it is narrower and more oval. The groove is lined by simple cuboidal epithelium. d. The External Spiral Sulcus (Plate XII, Figure D) The external spiral sulcus is the groove between the organ of Corti and the spiral prominence of the spiral ligament. It is lined by simple cuboidal epithelium. e. Border Cells (Figure D) These comprise a single row of cells which are located beside the inner hair cells. A number of slender processes are given off from the base of the cells. These processes join nerve fibers of the cochlear nerve to innervate the hair cells. Toward the internal spiral sulcus the border cells adjoin a single layer of simple squamous type cells. f. The Inner and Outer Pillar Cells (Figure D) The inner and outer pillar cells line the inner tunnel Of Corti. The cytoplasm of the cells is pale staining but the nuclei are darkly stained. The heads of the pillars combine to form a thick cuticular plate over which the tec- torial membrane lies. 64 g. The Tunnel of Corti (Plate XII, Figure D) The triangularly shaped tunnel of Corti is a canal which runs through the entire cochlea and is bounded by the tec— torial membrane and the inner and outer pillar cells. h. The Inner Phalangeal Cells (Figure D) The inner phalangeal cells form a row of cells on the inner surface of the inner pillars. The cells have darkly staining nuclei and pale staining cytoplasm. The tall slender processes of the cells continue to the surface and join the cuticle of the inner pillar cells. i. The Outer Phalangeal Cells or Cells of Dieters (Plate XIV, Figure D) The outer phalangeal cells are more numerous than the inner phalangeal cells. They support the outer hair cells, one outer phalangeal cell for each outer hair cell. These cells are tall columnar with large rounded nuclei and extend from the basilar membrane to the inner hair cells which they envelope. Slender processes from the phalangeal cells pass between the hair cells to the surface. The sur— faces of these cells contain cuticular plates which are con— tinuous with the cuticular plates of the inner hair and pillar cells. The cuticular plates of the outer phalangeal 65 cells combine at the surface of the cells to form the darkly stained reticular membrane which has openings through which the hairs of the outer hair cells project. j. Cells of Hensen (Figure D) These are many rows of tall columnar cells which are located laterally to the outer phalangeal cells. These cells extend to the basement membrane and have darkly stained nuclei and lightly stained cytoplasm. k. Cells of Claudius (Figure D) The cells of Claudius are a single row of low cuboidal cells with darkly stained nuclei. These cells form the lining of the external spiral sulcus and are the cells which are located laterally to the cells of Hensen. The cells of Claudius extend to the crest of the spiral ligament and are separated from this latter structure by a basement membrane. 1. The Cells of Boettcher (Figure D) The cells of Boettcher exist as a single row of low cuboidal cells which lie between the cells of Claudius and the basilar membrane. They have darkly stained nuclei and lightly stained cytoplasm. 66 m. Inner and Outer Hair Cells (Plate XIV, Figure D) The inner hair cells occupy a single row of cells be- tween the inner phalangeal and the pillar cells on the outside and the border cells on the inside. These are very large cells with flask shape. The entire cell is very densely stained and extends all the way from the basi— lar membrane to the tectorial membrane. The surfaces of the cells bear a thick cuticle through which the sensory hairs project to make contact with the tectorial membrane. A group of densely stained nerve fibers passes through the basilar membrane to enter the base of the inner hair cells. The outer hair cells are arranged in three, four or five rows from basal to apical coils and are located between the outer pillars and the outer tunnel of Corti. They are more numerous than the inner hair cells and are columnar rather than flask shaped. Unlike the inner hair cells, the outer hair cells do not extend all the way to the basement membrane but are suspended on top of the outer phalangeal cells which furnish their support. The outer hair cells are not as densely stained as are their supporting outer phalangeal cells. The surfaces of the hair cells contain a darkly stained cuticular plate through which the sensory 67 hairs project to the free surface of the organ of Corti. A group of nerve fibers reach from the inner hair cells across the inner tunnel to the base of the outer hair cells. 9. The Cochlear Nerve and Spiral Ganglion (Plates X, XI, XIII, XIV) The fibers of the cochlear nerve from the brain (Plate XVI) enter the bony modiolus at the basal coil of the cochlea. The peripheral processes of the cochlear nerve then pass through the osseous spiral lamina to the tympanic lip of the limbus spiralis. From here the nerve fibers penetrate the basilar membrane, where the total number of fibers become greatly reduced. These fibers then pass through the small openings in the basilar membrane before terminating in the inner and outer hair cells of the organ of Corti. The spiral ganglion lies in the spiral canal of the modiolus (Plates X, XI, XIV). This ganglion is made up of a number of darkly stained bipolar cells among which a number of nerve fibers are interspersed (Plates X, XI, XVI). The bipolar cells of the spiral ganglion (Plates X, XI, XIII) are much smaller in size than those of the vestibular ganglion (Plate IX) but the number of cells in the spiral I 68 ganglion is greater than that of the vestibular ganglion. The nuclei of the cells of the spiral ganglion are very distinctly seen and each cell contains one or more deeply stained nucleoli. The modiolar location of the spiral ganglion is richly supplied with blood vessels (Plates X, XI, XIII). SUMMARY AND CONCLUS I ONS The detailed histology of the inner ear of the dog has been presented. Fifteen labeled photomicrographs and three labeled drawings have been presented. In general, the histological structure of the canine inner ear follows the typical mammalian pattern. In agreement with the gross anatomical description of the inner ear of the dog given by Getty t g1, (1956) the cochlea of the dog contains three and one-fourth coils. Some of the important characteristics of the cochlea which have been observed in this study are listed below. 1. The osseous spiral lamina decreases in thickness from the basal to the apical coil. The measurements are: 95, 65, 52 micra respectively for the first three coils and it is only a small vestige in the last one—fourth coil. 2. The cochlear nerve decreases in diameter from the basal to the apical coil corresponding to the decrease in thick- ness of the osseous spiral lamina. 3. The basilar membrane is shortest in the basal coil where it measures 286 micra and longest in the apical coil where 69 70 is 500 micra. The average length of the basilar membrane in the second coil is 300 micra and in the third coil it is 497 micra. 4. The spiral ligament is widest in the basal coil and narrowest in the apical. The measurements are 315 and 78 micra respectively. 5. The stria vascularis is reduced in width from the basal to the apical coil but the average length is the same throughout. 6. The organ of Corti is smallest in the basal coil of the cochlea where it is 130 micra long and 19.5 micra wide. It is largest in the third coil where it is 208 micra long and 45.5 micra wide. The size of this structure is approximately the same in the second and last one-fourth coils. Various stains were used for demonstrating the general and specific histological details of labyrinthine structures. In this study it was found that Crossmon‘s modification of the Mallory's Trichrome stain was best for both general and Specific considerations. LITERATURE CITED Bailey, F. R. 1958. Bailey's Textbook of Histology. Re- vised by W. M. Copenhave and D. D. Johnson. Williams and Wilkins Co., Baltimore. Bast, T. H. and B. J. Anson. 1949. The Temporal Bone and the Ear. Charles C. Thomas, Publisher, Springfield, Ill. Bowen, R. E. 1933. The cupula of the membranous laby— rinth. J. Comp. Neurol., 58: 517-539. Buchanan, A. R. 1957. Functional Neuro—Anatomy. Lea and Febiger, Philadelphia. Crossmon, G. 1937. The modification of Mallory's connec- tive tissue stain with a discussion of the principles involved. Anat. Rec., 69: 33-38. Engstrom, H. and J. Wersall. 1953. Structure of the organ of Corti. 1. Outer hair cells. Acta Otolaryngo., 43: 1—10. Getty, R., H. L. Foust, E. T. Presley and M. E. Miller. 1956. Macroscopic anatomy of the ear of the dog. J. Vet. Res., 17, 64: 364-375. Am. GUild. S. R. 1927. Circulation of the endolymph. Am. J. Anat., 39: 57-81. Guyton, A. C. 1961. Textbook of Medical Physiology. W. B. Saunders Co., Philadelphia. Lurie, M. H. and N. E. Nachlas. 1951. The stria vascularis: review and observations. Laryngosc., 61: 989-1001. Maximow, A. A. and W. Bloom. 1957. A Textbook of Histology. W. B. Saunders Co., Philadelphia. Pearse, A. G. E. 1960. Histochemistry Theoretical and Applied. Little, Brown and Co., Boston. 71 72 Poltz, E. and H. B. Perlman. 1955. A histochemical study of the cochlea. Laryngosc., 65: 291-312. Polyak, S. L., G. McHugh and D. K. Judd. 1946. The Human Ear. Sonotone Corporation, Elmsford, N. Y. Smith, C. A., O. A. Lowry and Mei—Ling Wu. 1954. The electrolytes of the labyrinthine fluids. Laryngosc., 64: 141-153. Wersall, J. 1954. The minute structure of the crista ampullaris in the guinea pig as related by the electron microscope. Acta Otolaryngology, 44: 359—369. Wersall, J., H. Engstrom and S. Hjorth. 1954. Fine structure of guinea pig macula utricle. Acta Otolaryn- gology, Suppl., 116: 298-303. Wersall, J. 1956. Studies on the structure and innervation of the sensory epithelium of the cristae ampullares in the guinea pig. Acta Otolaryngology, Suppl., 126: 1—85. 73 PLATE I Horizontal section through the inner ear of the dog showing the dorsal and caudal semicircular canals with the cristae and the utricle with the macula. Crossmon's modification of the Mallory‘s Trichrome stain. 34X 1. Dorsal semicircular canal 2. Crista of dorsal semicircular canal 3. Membranous wall of utricle 4. Branch of vestibular nerve to macula 5. Endolymphatic space 6. Bone of labyrinth 7. Epithelium of macula 8. Otolith 9. Caudal semicircular canal 10. Crista of caudal semicircular canal ll. Endolymphatic duct 75 PLATE II Cross section through the dorsal semicircular canal showing the ampulla with the crista. Crossmon's modification of the Mallory's Trichrome stain. 35X Bone of osseous labyrinth Perilymphatic space Wall of membranous canal Endolymphatic space Cupula Branch of vestibular nerve Connective tissue of crista Epithelium of crista 77 PLATE III Section through the crista of the dorsal semicircular canal showing the sensory epithelium, connective tissue and cupula. Crossmon's modification of the Mallory's Trichrome stain. 310X 1. Outer portion of sensory epithelium 2. Hair cell 3. Supporting cell 4. Hair from hair cell 5. Nerve fibers 6. Connective tissue of crista 7. Cupula 79 PLATE IV Cross section through the crista of the dorsal semicircular canal showing how the epithelium is thick in the middle and becomes thin peripherally. It also shows that the thickest portion of the crista is in the middle and that it becomes thin in the periphery. Crossmon's modification of the Mallory's Trichrome stain. 230x H Cupula 2. Hair from hair cell of crista 3. Cuticular surface of epithelium 4. Hair cell 5. Supporting cell 6. Connective tissue of crista 7. Nerve fibers . . , I I 4 r .7; _ \f" I: ~‘ ’;‘v-.’.’ l‘ ’ .r'I 81 PLATE V Horizontal section of the caudal semicircular canal showing the crista and the nerve fibers to the crista. Crossmon's modification of the Mallory's Trichrome stain. 92X 1. Membranous wall of ampulla 2. Cupula Epithelium of crista Connective tissue of crista Nerve fibers to hair cells 83 PLATE VI Horizontal section of the inner ear showing the utricle, . 0 ... sacculus and caudal semiCircular canal. Crossmon s modi fication of the Mallory's Trichrome stain. l. Macula saccule 2. Bone of labyrinth 3. Membranous wall of utricle 4. Macula utricle Branch of vestibular nerve to macula utricle 6. Otolith membrane 7. Space for endolymph Crista of caudal semicircular canal Nerve fibers to crista of caudal semicircular canal 85 PLATE VII Horizontal section through the utricle showing macula utri- cle. Crossmon's modification of the Mallory's Trichrome ~stain. 92X Membranous wall of utricle Otolith membrane Epithelium of macula utricle Connective tissue of macula utricle Hair cell with hair Nerve to macula I V a . . — a u n ,- 87 PLATE VIII Cross section of the brain and inner ear of the dog showimg the vestibular nerve at the level of the restiform body. Crossmon's modification of the Mallory's Trichrome stain. l. 2. Restiform body Vestibular nerve entering brain Nerve to the vestibular mechanism in the ear Cerebellum Portion of temporal bone Cochlear nerve Spiral ganglion Osseous spiral lamina of basal coil of cochlea .. . L ,_.'.‘ -. . .‘ ~ . ‘fiy ka‘u;‘If .'.\s‘\\.\,: l I ‘l‘ ‘ ' ~\ \l ‘ *w 4 k“ 7 A 4:. I ‘ 89 PLATE IX Section of the internal auditory meatus showing the vesti- bular ganglion. Crossmon's modification of the Mallory's Trichrome stain. lOOX 1. Bone of internal auditory meatus 2. Fibers of vestibular nerve 3. Bipolar cells of vestibular ganglion 4. Large bundle of vestibular nerve fibers leaving vestibular ganglion 5. Blood vessel 91 PLATE X Cross section of the modiolus showing the osseous spiral lamina. Crossmon's modification of the Mallory's Trichrome stain. 88X 1. Modiolus 2. Bipolar cells of spiral ganglion 3. Blood vessels in modiolus 4. Osseous spiral lamina attached to modiolus 5. Nerve fibers in modiolus 93 PLATE XI Horizontal section of the osseous spiral lamina showing bipolar cells and nerve fibers of cochlear nerve.. Cross- mon's modification of the Mallory's Trichrome stain. 75X 1. Bipolar cells of spiral ganglion enclosed in myelinated sheath 2. Nerve fibers which pass through modiolus 3. Myelinated nerve fibers to organ of Corti 4. Bone of lamina 5. Blood vessels 95 PLATE XII Section through the cochlear duct. Crossmon's modification of the Mallory's Trichrome stain. 460x 1. 10. ll. 12. 13. 14. 15. 16. Limbus spiralis Vestibular lip of limbus spiralis Tectorial membrane arising from the vestibular lip Tympanic lip Osseous spiral lamina with cochlear nerve Blood vessel in limbus spiralis Internal spiral sulcus Spiral ligament Stria vascularis Spiral prominence Basilar membrane Vestibular membrane Cochlear duct Osseous spiral lamina External spiral sulcus Tunnel of Corti 97 PLATE XIII Cross section through the bony central axis or modiolus of the cochlea. Crossmon's modification of the Mallory's Trichrome stain. 88X 1. Spongy bone of modiolus 2. Blood vessels of modiolus 3. Spiral ganglion 4. Osseous spiral lamina 5. Nerve fibers from spiral ganglion passing through osseous spiral lamina 99 PLATE XIV Cross section through the organ of Corti of the third coil illustrating the different parts and some of the different types of cells which make up this structure. Crossmon's modification of the Mallory's Trichrome stain. Oil Immer- sion, 460x 1. Tectorial membrane 2. Inner hair cells 3. Outer hair cells 4. Hair from outer hair cell 5. Internal spiral sulcus 6. Limbus spiralis 7. Inner pillar 8. Outer pillar 9. Tunnel fibers 10. Basilar membrane 11. Outer phalangeal cells 12. External spiral sulcus 101 PLATE XV Cross section through the brain and ear of the dog showing the cochlear nerve to the auditory portion of the inner ear. Crossmon's modification of the Mallory's Trichrome stain. 34X 1. Restiform body 2. Cochlear nerve 3. Modiolus 4. Osseous spiral lamina 5. Spiral ganglion 6. Cochlear nerve to organ of Corti 7. Limbus spiralis 8. Vestibular membrane ..sr/ W‘- aura/r MIC HIGAIN STATE UNIVERSITY Ll BRA 1 HI I III IIH III III) llllll