A REGONAL ANATOMY or THE HEAD, NSCK, mom, AND ABDOMEN 06 TH! cmucmm, cmmmggmetu LANIGERA 3mm, WITH spew nuance To 114! mmm m M for tho Down 05 Ph. D. MICHQGAN STATE WES!” Rob»? Kcmeth Wolfe: 1955 u;.......... .&~>¢'é;'fl- 'nl 1:12.515 This is to certifg that the thesis entitled A regional anatomy of the head, neck, thorax, and abdomen of the Chinchilla, Chinchilla, lanigera langiera Bennet, with special referencerCMa figestive tract. Robert K. Wolfer has been accepted towards fulfillment of the requirements for _Bh.D_.____ degree in lonloggL. film Date £121.13,— 0-169 . .__.._W_.4_~ lla-_—~wmfi——#wm_-h-~_h - _—4_‘A IQM‘H : was A REGIONALMINIEOHI’OF THE HEAD, NECK, THORAXI, AND ABDOHEN OF THEiOHINCHILLA, CHINCHILLA LKNIGERA LANIGERA BENNET, WITH SPECIAL fiEfiERENCET TO‘THEIDIGESTIVE‘TRACT By Rebert Kenneth Wblfer A THESIS Submitted to the School of Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Zoology 1955 - y“ W "f ‘1 :7 1/ J ll, 5rd HMO Frontiapiece An adult I818 clhchflll, curring; Inigo-r3 13-13mm Benet Crown-rum) length, 31:0 millimeters; and over-all length, hOS millimeters. ii Frontispiece An adult male chinchilla, Chinchilla 1:11ng Inigera Benet Crown-rump length, 31“)? millimeters; and over-all length, 1405 millimeters. 15 ACKNOWLEDOIBITS The author is constrained to thank God, and to cannend the many individuals whose aid made possible the completion of this investi- gatiel. Te Doctor 11. 1. Fennell, major professor and chairman. of the guidance comittee , in appreciation for his continued encouragement, patience, supervision, and inspiration throughout this study, are dedicated the findings herein. The writer is likewise indebted to Dr. Robert C. Ball, Dr. William B. Drew, and Dr. Beinrick Stafseth, who so kindly consented to serve on the guidance canittee . Dr. H. Lois Calhoun deserves credit for making the facilities of the inatony Department available, for advice on the nanuscript, and for her participation in the preliminary and final examinations. Particularly salutary have been Dr. H. R. Hunt, retired head, and Dr. Karl A. Stiles, present head of the 200109 Department. Hrs. Bernadette Henderson (Kiss Hac) shall long be remembered for her skill- ful counseling of graduate students in Zoology. Richard D. Moore of the anatomy staff, has willingly lightened the acadenic burdens of the author during the progress of the inquiry. Mr. William Iouatt of the Hichigan Department of Conservation prepared the frontiep’ie'eeo Much is owed to the nmerous investigators who have published papers , nonographs , and texts on related anatomical subjects . Unpub- lished theses of Dr. Nicholas Hiseres, Dr. Harold Orwell, and of Dr. Thomas Jenkins, have been referred to repeatedly. Dr. Jenkins also afforded valuable advice on nany occasions . The Kellog Sales Cmpany of Battle Creek, Michigan, suggested the problem, furnished necessary financial support, and arranged for many of the specimens examined. Growers who have delivered specinens through the Kellog Sales Calpany, are as follows: 141‘. Dominic Circosta Hichigan Branch of the National Chinchilla Breeders Association Southern Michigan Chinchilla Ranch The Chapman Chinchilla Ranch, Inglewood, California 141‘. Henry 0. Trinklein, owner of the Trinklein Chinchilla Ranch, Saginaw, Michigan provided several valuable animals, and proffered iv his astute observations of the habits of living chinchillas. His out- standing assistance cannot be overestinated. Hr. Edwin H. Ciolek, grower, of Lansing, Michigan also donated a specinen, as well as did others. The Michigan State University Depart-_ nent of Physioloy supplied two specimens . Mr. Barry Zerbo, Livonia, Michigan, nsnber of the Rational Chinchilla Breeders of Anerica, Inc., supplied three nales and three fenales for study, at the request of the national office. Mr. B. Jones Salbach, Santa Rosa, California supplied six aninals, and Hr. E. L. Larsen, Ovid, Michigan supplied two pairs and one nale upon request of the Chincfllla Association of Anerica. The Chinhilla Association of Anerica, whose badqu is located at Santa Rosa, California, has been very helpful in nany ways, and especially by contributing a subscription to the national journal, The Chinchilla News, and by arranging for specinens. At various nestings of certain branches of both national chinchilla organisations, tb author was invited to report on the development of his research, and at such gatherings learned sue of the problens of applied chinchilla norphology . The assistance of the Rational Chinchilla Breeders of Anerica, whose headquarters is in Salt Lake City, Utah, has also been incalcul- able . The association arranged for nany specinens through various branch numbers, granted the author free access to research files of the national office , and provided various research bulletins. The association also supplied sons Kodachrone slides for use in a report on the present research given before the 1955 session of the Michigan Acadeny of Science, and granted financial help for the preparation of specinens by the General Biological Supply House , of Chicago, Illinois . The tedious task of inking the drawings for duplication was perfumed by the author's wife. 01' vital inportance, the author's wife, Shirley, her nether, and his parents and children were responsible directly and indirectly for essential comforts, hoalth, and fortitude during the entire period of this undertaking. Acknowledpents would be inconplete without a connendation for the painstaking duplication of the nanuscript by the Steinhoff Studentservices of Brighton. “Chum!- CURRICULUM VITAE Robert Kenneth Wolfer, the ,9th of 15 children, was born in Pekin, Illinois, in 1920. His early education.was obtained in that city, where he was graduated from Pekin.Community High School, in 1938. In 19M, he was graduated from Emanuel Missionary College, Berrien Springs, Michigan, with a Bachelor of Arts degree. While a senior stu- dent at that institution he assisted in the Biology and Chemistry laboratories. During the intervals between college enrollnents he acquired experi- ence and skill.in*various trades; especially in welding, plumbing, and electrical work. He was a graduate assistant for nearly two years in the Department of Zoology, Michigan State University, and accepted his present position as Instructor in the Department of Anatomy, the fall of 19149. He served as a Seasonal Ranger Naturalist at Yellowstone National Park, Wyoming, during the sununer of 19514. In the summer of 1955 he studied Human Gross and Neuroanatomy at the University of Michigan Medical School, inn Arbor. The author has been appointed as an Instructor in Anatomy by the Des Hoines Still College of Osteopathy and Surgery, Des Moines, Iowa, which duties are to commence September 1, 1955. The author is a,member of the society of Sigma Xi, of the American Association for the Advancement of Science, of the Michigan Audubon Society, and of the Associated Nature Clubs of America. vi On May 16, 191:3, he married Miss mogene Shirley Strickland, registered nurse, and is the father or two daughters, ages three and two , respectively . vii lmlmmrmormm,m,mu, mam (r was cmcmna, camcm menu mmm 3mm, ma srmm. W013?) Gmmc'r By Robert Kenneth Welter AN ABSIRLCT Suhitted to the Schoel of Graduate Studies ef Michigan State University of Agriculture and Applied Science in partial mlrinnent ef the requirements for the degree of DUSTOR a" PHILOSOPHY Department of Zeeley Year 1955 Lppreved 62"”ij _ : _ viii ABSTRACT Although the locomotor apparatus of rodents has been the subject of nmmerous investigations the gross anatomy of the digestive tract has been neglected. The present study represents an initial contribution to the detailed knowledge of the digestive system of the chinchilla, Chinchilla lanigegg laniger; Bennet, a hystricomorph rodent. Twenty-five adult animals were dissected and sixty-four drawings made of various dissections. For tepographical reasons, the major axially-placed organs of the other body systems have been illustrated and briefly described. The oral cavity presents a trichous post-incisal subdivision. The teeth are twenty in number, are monophyodont, and all erupt contin- uously. The tongue presents a wide variety of papillae . The pharynx is chiefly nasopharynx and a laryngeal pharynx is absent. The esOphagus is not noticeably modified. The stomach is relatively unsacculated. It is not possible to dis- tinguish.any definite subregions of the relatively long small.intestine. Numerous macroscopic lymphatic nodules are present in the wall. The large intestine has an expanded spiralled and sacculated cecum , a.long large colon and a long and highly coiled small colon. ‘Whereas the greater portion of the small intestine lies sinistrally, much of the small colon is located to the right of the mid-line. The rectum is only a relatively straight and uncoiled terminal segment of the small colon. The large intestine is noticeably longer'by about two-thirds than the small intestine. Various myological observations stand at variance with the find- ings of Wood and White (1950) concerning certain muscles of the present species . CONTENTS I. mTRmoTIONOOOOOOCOOO00.0.000.0.00.00.00.00.0000000000.00.. II. “TmmsmMETHODS.OCOOOOOOOOOOOOOOOOO OOOOOOOOOOOOOOOOOCO III. Tm can CAVITY.OOOOOOOOOOOOOOOOOOeOOOOOOOOOOOOOOOOOO0...... ‘0 Th. Lip, “d Cheebeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 1. The Lip-00.0....OCOOOOOOOOOOOOOOO00......0...... 2. T119 cmOkaOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 8. The vestibule..0...0....OOOOOOOOOOOOOO0.0.0.0....O0.0. 1. Tm Incj'm vestibul.OOOOCOOOCOOOOIOO...00...... 2. The Molar Vestibule............................. C. The Postincieal Recess................................ De The oral 0‘71” P1.0pereeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 1. Tm PdauOOOOOOOOO0.0.0.00...OOOOOOOOOOOOOOOOOO 2. Tm FlooroOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO. 3. The Wall of the Oral Cavity..................... h. The Teeth....................................... O Tm Tong...OOCOOOOOOOOOOOOOOOOO0......O...00.0. 3. Tm mivary mm.OOOOOOOOOOOOOCOOOOCOOOCOOI.0...... 1. The Pmtid Glan(1eeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 2. The Mom 618“deeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 3. The “WW mad.0000000000000000000.00.00 h. The Candal, Middle, and Accessory sublingual mdsOOOOOOOOOOOOOOOOOOOOO0.000000000000000. S. The Roetral Sublingual Gland F. The Muscle: of Mastication............................ 1. The Muscles of Facial Expression................ 2. The Prime Muscles of Mastication................ U1 I'e TIE PmmeOOOooeeeeee eeeee e eeeee see.oeeeeeeeeonOeeeeooon 11,4 ‘e The unopmanOeeeeeeeeeoee'eeeeeeeeeeeeeeeeeeeeeeeeee B0 The MWOeoeeeeeeeeeeotoeeeeoeooeoeoeeeooeeeeeee 0. The Muscles of the Pharynx '. TIE NmK0eoneeeeeeeeeeeeeeeeeeeoeeeeeeeeeeeeeeeeeeeeeeeeeee '1. TE THOWOOCOOIOOCOOCOOCOOOOOOOOOOOOOOOOOOOOOCOOOOO00...... ‘0 Th. "all or we ThomooeeoooeeeeeeeeeeeooooeeeeOeeee B. The Major Organs of the Thorax........................ 117 117 117 123 125 .125 128 zom'm'rs - Continued Page ’II. Tm EmpmwSOOOO0.....COOOOOOCOOOOOO.IOOOOOO0.0.0.0....00. 137 A. The Cervical Portion of the Esophagus................ 137 B. The Thoracic Portion of the EBOphag'nl................ 1140 C. The Abdominal Portion of the Esophagus............... lhO III. Tm “Damn CAmTOOOOOOOCOOOOOO.OOOOOOOOOOOOOOOOOOOOOOO. ”‘3 A. The Walls of the Abdominal Cavity.................... 1243 l. The Ventrolateral Wall of the Abdominal Cavity. lid; 2. The Cranial or Rostral Wall of the Abdolinal c‘fityeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 155 3. The Dorsal Abdominal Hall...................... 159 h. The Caudal Abdominal Wall 160 B. The Non-Digestive Organs of the Abdominal Cavity..... 160 1. The Spleen..................................... 160 2. The Female Reproductive Organs................. 166 3. The Male Reproductive Organs 173 h. The Excretory Organs of the Cinnchilla......... 182 5. Other Non-digestive Abdominal Organs........... 1814 C. The Digestive Organs of the Abdominal Cavity......... 18h 1. Th. “WChOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOC... 188 2. The Intestines and Comm 192 3. Tm Pmcmu...O.0.00.0000...OOOOOOOOOOOOOOOOO. 203 h. Th6 uverOOOOOOOOOOOOOOOOOOOOOOOOOOCOOOOOOOOOOC 208 5 . The Peritoneal Reflections to the Abdominal Digestive Organs 212 1. WIOOOOOOOOOOOOOOeeeeeeeeeeeeeeeseeeeeeeeeeeeeeeeeeeeoee'221 ITEMNRE CITEDOCQOOOOOOOOOOOOOOOOO0.0.0.000...OOOOOOOOOOOOOOOOO 22h LBLE LISI‘ CF TABLES Page The Lengths of the Twenty-Five Longest Mystacial 'ibri.'“OOOOOCOOOOOOOOCOOOOOOOOOOOOOOOO0.0.0.000...0.0.0. 18 The Lengths of the Non—Mystacial Vibrissae................ 19 The Color of the Twenty-Five Longest Myetacial Vibrissae . . 20 Measurements in Millimeters of Molars Illustrated in Pima Bevan md TmlveOOOOOOOOOOCOOOOOOOOOOOOOOOOCOOOO. uh xiii EURE l. 2. 3. h. 5. 6e 12. 13. 1h. 16. LIST (1" FIGJRES Page The Chinchilla Muzzle with the Labia Closed...... .......... The Chinchilla Muzzle with the Labia Partially Retracted... The Chinchilla Muscle with the Labia Fully Retracted and tho “Nth wemd widelyeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeoee W‘tion 0: th. ruin '1br1.mOOOOOOOCOOOOOOOCO .0 00...... The Distribution of the Twenty-Five Longest Mystacial 'ibmmOOOOOO......OOOOOOOOOOOO...OOOOOOOOOOOOCOOOOOOOOO. A Side View of the Head of the Chinchilla with the Left Cheek Removed to Show the Palate, the Inner Surface of the Right Cheek and Fences, and the Floor of the Mouth......... A Ventral View of the Palate of the Chinchilla... ........ mtline M‘flng. or the Right Incjisor‘.OOOOOOOOOOOOOOOOOOOO A Lateral View of the Skull with the Mandible Removed and the Babedded Portions of the Teeth Outlined................ The Medial Surface of the Right Half of the Mandible With the E‘sbedded Portions of the Teeth Outlined and the Proximal End of the Incisor Exposed........................ Drawings of the Occlusal , Mesial, Distal, Buccal, and Lingual Surfaces of the Right Mandibular Molars............ Drawings of the Occlusal, Mesial, Distal, Buccal, and Lingual Surfaces of the Right Maxillary Molars. . . . . . . . . .. .. A Side View of the Skull Showing the Curvature of the Molars and the Position of the Incisors when the Respective Molars Occlude 00......0.00.0000...0.00.00.00.000.00.0000... A Frontal View of the Upper and Lower Jaws (Incomplete) Showing the Lateral Curvature of the Molars and the Relative Position of the Basal or Bottom Planes of the “aluaoeeeeeeeeeeeeeeoeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee ; Diagram of the Mamer of Occlusion of the Various Molar eeth ......OOOOOOOCOOOO.....OOOOCOOOOOOOOCOCOOOOOOOOOOOCOOC The Dorsal surface of the Tongue xiv 10 10 10 15 17 26 28 3h 38 38 143 1:6 148 1:8 138 53 Sf 01" FIQJRES - Continued 17. 18. 19. 20. 21. 22. 23. 2h. 25. 26. 27. 28. 29. 30. A Ventral Dissection of the Tongue......................... A Cross Section of the Head to Show the Tongue and Oral C‘dty RehtiOMWSOOO‘OOOOOOOOCO...OOOOOOOOOOOOOOOOOOOOOOO A Parasaggital Section of the Head to Show the Tongue and t“ ’WWOOOOOOOOOCOOOOOO00............OOOOOOOOOCOOO0.... The Right Parotid , Submaxillary, and Buccal Salivary Glands A Ventral View of the Head to Show the Platysma Muscle and Other Structures Related to the Underlying Submaxillary WOODCOCOOOOUOOOOOOOOI.......OOOOOOOOOCCOOOOOOOOOOOO... A Ventral View of the Head and Neck to show the Parotid, the Submarillary , and the Caudal and Middle Sublingual (Bands after Removal of the Platysma Muscle................ The Ventral Surface of the Read Showing the Submaxillary and Sublingual Glands Displaced Laterally, and the Origin and Course of the Submaidllary Duct to the Level of the Myloluoid Muscle A Ventral View of the Read, the Sublingual Glands, and the Termination of the Sumaxillary Duct....................... A Lateral View of the Read and Neck to Show the Various Muscles of Facial Expression and Various Underlying StmctmIOOOOOOOOOCOO....OOOOOOCOOOOOOOO000.00.00.00...... The Right Side of the Front Half of the Skull to Show the Deep melee Of Paid MrQBSi'onOOOOO0.0000000000000000... A Lateral View of the Skull to Show the Superficial Portion of the Maseeter Muscle A Lateral View of the Zygomatic Arch and the Intermediate Portion of the Masseter Muscle A Lateral View of the Zygomatic Arch and the Posterior Deep Portion of the Museter Muscle A Lateral View of the Skull to Show the Anterior Deep Portion of the Masseter Muscle and the Temporalis Muscle... 31. A Lateral View of the Skull with the Caudal End of the Zygomatic Arch Removed to Expose the External and Internal PtoWEOidMMC10.........OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOIOO Page 53 65 73 76 79 8h 88 91 100 103 106 109 112 ST CF FIGURES - Continued Page 32. 33. 3h. 35 . 36. 37. 38. 39. 1:0. 1:2. 1‘3. bh. 1:5. MS. The Dorsal Surface of the Pharynx Showing the Intrinsic and Extrinsic Muscles and also the Proximal End of the hopm ‘m Tr‘cm‘OOOOOOOOOOOOOOOOOOOOOOOOOOOO000...... 119 The Lateral Surface of the Pharynx to Show the Attach- ments or tm Pm........OOOOOOO...0.0.0.0....00.00.... 119 The Superficial Structures of the Ventral Surface of the NOCk‘mche’tOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO. 127 A Ventral View of the Thymus Glands, the Lungs, and the EMOOCOOOOOOOOOOOOOOOOOOO.0.00.0.0...00......0.0.0.0.... 130 A Ventral View of the Deeper Structures of the Neck and CheatOOOOOOOO......OOOOOOOOOOOOOOOO......COOOOOOOCOOOOOOOO 133 The Relation of the Trachea and Lungs to the EsOphagus.... 135 A Ventral View of the Aorta and Esophagus................. 139 A Cross Section of the Thorax at the Level of the Right ventflOIOOOOCOCOOOOOOOOO0....00.0.0.0...0.0.000...0.0.0.9. 11:2 The Outer Layers of the Ventral Abdominal Wall of an Adult Femfle cmchmaOOCOO......OOOOOOOCO......OOOOOOIOCOOOOOO 1’46 A Deeper Dissection of the Ventral Abdominal Wall to Show the Internal Oblique, the Transverse, and the Rectus Abdominis Muscle, and also the Scrotal Diverticulmn.. . .. . . 1149 The Abdominal Surface of the Diaphragm, the Surrounding Chest Wall, and the Dorsal Body Wall and Lumbar Spine..... 151; The Outline of the Thoracic Structures Related to the Diaphragm as Seen from the Abdominal Surface of the Diaphragm; also the Major Vessels and Nerves Related to the Dorsal Abdominal Wall-................................. 157 The Relationships of the Stomach, Pancreas, Spleen, Kidney, am hft mm mandOOOOOOOOOOOOOOOOOO0.0.000... 162 The Ventral Surface of the Spleen, the Mesosplenic Attachnent Outline, and the Blood Vessels of the Region... 165 A Ventral View of the Reproductive and Excretory Organs of a ng‘mt FemdeOOOI.......OOOCOOOCOOCCO.....OOOOOOOOOOCO 168 ST OF FIGURES - Continued Page L7. The External Genitalia of the Female Chinchilla as Seen rm BehindOOOOOOOOOOOOO000......COOIOOOOOOOOOCOOOOOOOO... 172 1:8. A Profile View of the Female Cenitalia and an Outline of the ABSOCiated “MSOCCCC0............O...’.OO.....COCC... 172 19. A Ventral View of the Male Urogenital Organs (The Urinary Bladder has been Opened, the Pubic Symphysis Removed, and the Left Thigh Amputated and Pulled Laterally to Show the Deeper Glands on the Left Side............................ 175 50. A Ventral View of the External Genitalia of the Mile cmnchmaOOCOCOOOCOOOOC00............OOOOOOCOOOOOOOOO.... 179 51. A Ventral View of the Erect Penis with the Prepuce EflractedCCCOOOCO......OOOOOOCOOCOCOCO0.0....0.00.00.00.00 179 52. The Terminal Portion or Clans of the Penis to Show the Position of the Urethra, Os Penis, and Sacculis Glandis... 181 33. A Diagramatic View of the Ventral Surface of the Abdominal Digeative organ80000..........0.0.00.0.........OOCOOOOOOOO 187 Sb. A Ventral View of the Regions of the Stanach.............. 190 55. TM matric Falda or R‘lgaOOOOOOOOOO‘COOCCOOOOOOO0.00.0.0... 1% 56. A Semidiagramatic Illustration of the Small Intestine and Its BIOOd swplyCO0.0......COOOOOOOOO.......OCOOCOOOOOOOO 195 57. A Ventral View of the Large Colon and Related Structures. . 199 58. The Snell Colon and Related Structures.................... 202 I 59. The Left and Princin Pancreatic Mass , Showing Foliatiorg 205 60. The Right Pancreatic Mass , Showing Foliation. . . . . . . . . . . . . . 207 61. A Ventral View of the Liver ......OOOOOOOOCOOOOOOO00.0.0.0. 210 62 . The Blood Vessels of All Except the Cranial Subdivision of the Right Lobe of the Liver eeeeeeeeeeeeoeeeeeeeeeeeeoee 21L 63. The Blood Vessels of the Cranial Subdivision of the Right Lobe of the Liver ....00............OOOOOOOOOOOO0.0.00.0... 216 61.1 . The Epiploic Foramen and Related Structures . . . . . . . . . . . . . . . 219 xvii I . INTROIXJCTION Kellog (1953) naintained than-e chinchilla is endemic to South series. This species was introduced into the United States in 1923 by Lthias P. Chap-an who obtained eleven aninals tron Chile for establish- ant of the first foundation stock on the North Anerican continent tor sinchilla men-g (National Chinchilla Breeders, 1953) . Since the species was first introduced breeding has become an :tensive and prosperous industry. Brenon (1952) estinated the value I.’ eninals and equips-t, in less than twenty per cent of the industry I the United States and Canada, to be about five million dollars. It was to be expected that with bevy inves‘hlents in both aninals :dequipent,therewouldbeanimreasedinterestinallaspectsof pth pure, and applied science dealing with chinchilla taming. During the course of this study the author reviewed approxinately no thousand referemee to the chinchilla in the files of the National tinchilla Breeders of Aneriea, at Salt Lake City, Utah. The najor rtion of the articles were concerned with the various problens associ- ed with chinchilla culture. A snaller nunber were concerned with cidental anatmical itens. The paucity of scientific publications on chinchilla norphology is t; a reflection of the attitude of breeders . Cassini (19514) inspected .r'ioue breeding establish-ants in all regions of this country and excluded that ranchers were bully aware of the need for additional for-ation on chinchilla norphology . Publication of such observations 3 an ilportant factor in the decision of the Xellog Sales Company of .ttle Creek, Michigan to support this investigation. Breeder interest was only one factor in notivation of this study. man (191:2) naintained this vast field of unsolved problens remained to r worked out by enbryological and anntonical procedures rather than V experilental investigations. Several of the problus related to the Linchilla rennin to be worlmd out, i.e., the relationship of chinchilla > other species in the game, the Histriconorpha in general, and the .stribution of the suborder in South Anerica, Africa, Dix-ope and North Ierica. Only a linited number of investigations have been concerned with prphological features of the cMnchiDa. Imel (1826) described sene .’ the features of this species. Bonnet (1829) described this species I g-eat detail and a portion of the naterial which he published was .sed on observations of living specinens. Iarrel (1831) nade an ditional anatonical contribution to chinchilla norpholog . Bonnet 833) characterized the sunny Chinchillidae. have years later, Bonnet 835) nade additional counts on the fanily chinchillidae. Owen's (1839) report was concerned with the anatcwr of various gan systems. Flower and Leydekker (1891) and Autrons (1906) nade ditional consents on the anatany of the chinchilla. Bic kel (1931) also neidered the chinchilla in his report. More recently reports dealing prinarily with the anatay of the Boise have appeared in the literature. Detwiler (19149) described the eye of the chinchilla. Wood and White (1950) confined their report to the W systen. lewberne (1951) considered various gross, microscopic, and physiological features in this species. Journeay (19h?) prepared an introdnctory atlas concerning the reproductive antes. Wilcox (1950) described the skin and hair, and Brennn (1952) briefly surveyed the various body organs. Ballard and Parkinson (1953) described the nale reproductive trust. launan (19514) studied the nature of hair coloration. The United ststes resting cw (195k) investi- gated certain plusical strengths of the hair. Shackelford and Boos (1951:) described the gross anatoq of the genital system, two endocrine glands, and also listed body weights of chinchillas. wood (1951) indicated that there was a scarcity of information on Insoles , bones, teeth, and other internal structures in most nenbere or the suborder Hystriconorpha. Allen (19112) referred to the chinchilla as Chinchilla laniera .1Iniigera Bonnet. As this nanologist has set a precedent, the author ht: enployed the sale scientific nane. Shackelford and Boos (1951;) used Chinchilla laniggra Bonnet, with no subspecific designation. They also media next nest cos-on chin- chilla found in this country, the brevicaudata, as Chinchilla brevicau- at; waterhouse. Others refering to the fore studied in this work as Skinchiiis laniggra were Osgood (19in). Detsiler (1919). Brenon (1952) and Kellog (1953) . Papers by Prell (19311) and Osgood (1914].) rather canpletely dis- cussed the scientific nane of the chinchilla, beginning with Hollina's <_— paper of 1782 (cited by Osgood, 1191411). Osgood was of the opinion that the naming of the chinchilla is a very delicate one, with much row for difference of opinion. The satisfactory naming of this animal is thus another of the problens which denmds in part , anatonical resolution. In behalf of general zoological information, careful studies should be nade on this fern. Albert (1901) recognised that the chin- Chilla was rapidly nearing extinction in South Anerica and noted that on the twenty—fifth of October (1900) the Resident Agent of Antofagasta, Mr. C. H. Sayago, directed a letter to the Hinistxy of Industry asking for the couplets prohibition of hunting and trapping of the aninal for a period of five years to avoid it 's extinction. Von eion (1928) dis- cussed the sane pmblen. men (1912) included the chinchilla esong the extinct and vanishing male of the western buisphere. The de- velop-out of a sound pelting progran meld doubtless prolong the survival of this species . but in event such does not naterialise, it is possible that the chinchilla fill becaa an eninal of the past. the _ present work constitutes a partial anatomical record of the chinchilla. Finally, mnerous diseases affect the chincmla, sate apparently couch and pathogenic to nan (Kennedy. 1952, and cutter, 93 5.1.. 1953). Anatonical studies would be useful as a standard of cauparison for the study of the various norphologcal changes due to disease . '1 It is the purpose of this study to present a description of the regional anatony of the digestive tract of the chinchilla, designated for the present as Chinchilla laniggra lanigera Bonnet, and known in general by the industry as Chinchilla laniggra, or chinchilla. III! .III Ill-III" lllll‘fI This workisnotacomparative studybntsone reference isnadetothe anatomical arrange-ant of cannon nmals as an aid in interpretation of the findings. Selected articles having a bearing on this work are included in the list of references . II. mm All) HETHODS Eighteen chinchillas (Chinchilla 35259.55 M); nine Isles and nine females, were embalned and the blood vessels injected with colored latex at the General Biological Supply house , Chicago, Illinois . The above concern also prepared ligamentons skeletons of a ale and a fade chinchilla. . Nine males and three females were sacrificed and preserved in an embalning fluid bath until dissected. One specimen was fresh-frozen and than cross-sectioned serially at Cppmzlnatel: one-fourth inch intervals , for studies on tepographical relationships. Freshly killed specimens were used for canparison with various dissections of mbalned animals. Additional specimens, for in amber, and ranging from two hours Poet perm to several weeks in age, were preserved in embalning fluid find later dissected to determine the general arrangement of the digestive tract in mature chinchilla . Six chinchilla , four males , and two {males were sacrificed and the digestive organs immediately placed in formalin-acetic acid-alcohol fixing solution for histological studies. A survey of each part or the digestive tube, and of each digestive gland was made in order to verify wrath gross interpretations, but no detailed histological study to: “Ede. Six live animals were observed at frequent intervals throughout Lpproxinately one year, as a means of observing the various habits of captive cMnchinu, as well as for studying dietary responses. Sixty-four figures of dissections and four tables fortify the VIII-ions descriptions. The figures are cupies of india ink tracings of Original drawings nude at the time of dissection. ho attelpt was made to conform to exact enlargements, but the various organs of am figure are drawn proportionately. The greatest enlargements do not exceed about four tines the actual naterial illustrated but most drawings are of a lesser nagnification. Sons actual neasuraents, in millimeters, of all digestive organs and major related organs are included as a guide to cmparative sizes. The various structures illustrated in the figures are labelled with letters or numerals placed on transparent overlays , and a key accompanies . In the text, the number of the figure or figures which includes the Structure being discussed is included with the description. A dissecting microscOpe was employed as a means of checking dissect- >d structures, especially the various ducts of glands, and finer vessels Ind. nerves. Il‘he microscOpe was equipped with 101 ocular lenses, and >Oth 11 and 3X objective lenses. The entire contents, including illustrations, were duplicated by 'he (1in dye wet process of direct-positive contact photoprinting. III. THE ORAL CAVITI Tin oral cavity constitutes the cephalic portion of the digestive system. The digestive tract of the chinchilla extends from the labial introitus to the anus, and is nodified grossly into the oral cavity, pharynx, esophagus, stusach, intestines, and anus. major glands associated with the tract include the liver, pancreas, and salivary glands. The various non-digestive structures presented in this account are included for topographical reasons . i. The Lips and Cheeks 1 . nil-in: The labia oris of the chinchilla are canplexly folded and capable of capletely (fig. 1) or variously (figs. 1, 2 ad 3) covering the incisors and the cephalic end of the oral cavity. When the lips are retracted, their angles (connissurae labia oris) can be seen to extend caudal to the incisors, and are located in the region of a broad diastena between the incisors and molars. The lips assist in fanning a post-incisal subdivision of the oral cavity which presumably acts as a recess for particles freed during the act of gnavdng. The pelage is modified near the labial margins by a reduction in Size, amber, and coloration of the hairs. The hairs nearest the FICDRE 1. FIGURE 2. FIGIRE 3. THE cnmcm 1mm WITH THE LLBIA CLOSED 1. interior name 2. Median raphe 3. Superior labiun h. Inferior labium THE CHINCHILIA 1112213 ms THE LiBIl PARTIALLI WED l. Gingiva 2. Superior incisors 3. Inferior incisors h. Post-incisal recess TIE CHDICHIILL MUZZLE WITH THE 1.an FULL! WE) AND THE HWTH WEED mm 1 . Inflezun pellitun superior 2. Menu pellitu: inferior 3. Superior circuincisal vestibule h . Inflesun pallium superior raphe 5. Aperture of oral cavity proper 6. Bristles of buccal bristle pad 7. Dorsal of tongue 8 . Inflexun pellitun inferior cleft 9. Inferior circuIIincisal vestibule 10 ”I M ”"Wr“iii-i WW \sg «W/ \1‘: 6’/// \“ '— : I \ ...__ 77.. . vb", P, . .7 _,_ ‘ " ‘ .J - V1 ‘ , . h i ”l: .1“ 1: m ... ... 45‘1" .1, y 3“ 'L. ‘l ' “A -' n r «J W 10 w / a; 0 r11 m n\.u\ /u \\ a I‘ K no. [N r I‘ r M C \\ 4 \ \s .2 rima oris are mostly white and lack color bands. This sparce distribu- tion of short, fine hairs prevailed about the inner margins of the lip, and at the buccal bristle pad (fig. 3) the hairs participated in the tuft. ‘ The superior labilm is partially cleft at the midline (fig. 1), the dorsal uncleft portion being defined into right as! left portions by an indistinct median raphe. The cleft portions nest in front at an acute angle directed toward the nasal septum, the upper incisors being exposed in the intervening interval. The borders of the upper lip are folded inmdly to entirely sur- round the gingivae of the respective incisors (figs. 2 and 3). The edges ' of tin infolded portion or inflow pellitus (Weber, 1927) of apposite sides partially has at a short median naphe imediately caudal to the incisors. The circuincisal border attaches It the line of reflection of the gingivae and surrounding mucous membrane thus defining a shallow isolated vallate depression herein referred to as the superior circum- incisal vestibule (figs. 2 and 3). The inferior labium is uncleft, there being however an indication of a median raphe. The margin presents inward projecting circumincisal lobes similar to those of the upper labium except that they do not fuse caudal to the incisors . The margins of the lobes do not fuse to the gingivae of the lower incisors, and hence there is only a functional and not a fixed isolated inferior circumincisal vestibule . The pelage modification resembled that described for the superior labiun. The apex of the tongue appeared 12 to rest in a fossa defined by the infolded lobes of the lower lip. The lower lip is bound to the gingivae by two frenulae, one on each side of the median line . The post-incisal lobes of the labia, the apex of the tongue, and a fleshy tubercle on the mid-dorsal diastemal portion of-the hand palate, appeared to rest in contact, thus effectively separating the oral open- ing and the incisors from the oral cavity proper. The apparent functional simificance of this arrangement is to pemit extended action of the incisors for gaming without constantly exposing the general oral cavity to the freed particles. The interpretation is supported by an opinion of the function of this arrangement in rodents in general as stated by Beddard (1909). In life, there is considerable nussitation accentuated by mandibular excursions, acconpanied by rapid vibration of the mystacial vibr issae. 2. The Cheeks The cheeks or buccae are defined as the fleshy portions of the sides of the face by Dorland (19147). The definition referred to is more inclusive than that given for the cheek by various other authors . Major anatomical works are somewhat vague as to the limitations of the cheek (Gray, l9h2 , Buchanan, 1953 , and Cunningham, 1951, for the human; Miller, 1952, for the dog). Reighard and Jennings (1935) described the cheeks of the cat as extend- ing from the lips to the mi of the mandibles. Sisson and Grossman (1953) stated that the cheeks of the domestic animals formed the sides 13 of the mouth, were continuous with the lips craniad, and were attached to the borders of the bones of the Jaws. Webster's New International Dictionary (who) indicated that the cheeks ofman and othernmlsare the fleshywallor side of the mouth, the side of the face below the eye, and above and to the side of the mouth. In the present study the cheeks are considered to include all structures frets the integument to the mucous mbrane of that portion of the face which bounded the mouth laterally from the lips to the fauces and to the pharyngeal entrance . The external surface of the cheek is covered with fur similar to that of the general body surface . In addition, prominent mystacial vibriesae are present at the labial end of the cheeks (figs. 1: and S). The vibrissae are prominent features of the chinchilla muzzle. Wilcox (1950) did not describe the vibrissae in detail and did not mention the vibrissal groups in his description of the chinchilla. Wilcox, £3219.- , found that the vibrissae were long heavy sensory hairs completely separated from one another. In the present specimens this was true only for some mystacial vibrissae, whereas many were paired in the follicles, and in none of the specimens examined was there a complete lack of paired vibrissae. . Certain generalizations can be mde concerning the specimens studied. There is no apparent significant sex related specialization of the vibrissae. The! are not of equal length and the largest and the thickest are located at the caudal portion of the group. lb FIGJRE 14. LOCATION or rm: mom. umussu:fl l. sepercilliary 2 . Genal 3. Sablental h. Hystacial 5} Interramal. * Pocock (191k) . Os... . . o. o. o ....-.s 1"" it, _ w v n . _. l ... d i V. I k b ' .-. . , ._~‘ I and 16 FIGURE 5. THE DISTRIBUTION or THE m-FIVB WGESI' 1118!]an VIBRISSLE l. Largest; and 2S, shortest 1r. Male 1, right side 11. Male 1, left side 2r. Male 2, right side 21. Male 2, left side 3r. Female 1, right side 31. Female 1, left side hr. Female 2, right side 141. Female 2, left side B. W end of group C. Caudal end of group 3. Outline of area cmhinhg the majority of vibrissae shorter than the twenty-five longest vibrissae (usually about double the amber of longer vibrissae) .. Two per follicle; x-shorter than first 25 Note: The numbers of the longest vibrissae indicated in this figure, correspond to those in Table I. Table I gives the length for each vibrissa to the nearest half millimeter. 17 \‘|",I ‘ _ , r ,. la n I. , r a e a t. _ ,3 a Earth. I l . e r p a . a .r ,fl.—Jtr 1 I x a rib I \ II o J I . \ I ‘ 3 ~. I I II \ [I k\ III s‘\\ [I .,\ (I! [S L“ lllll R R a \ """ R \ l \\ I; IIIIIIIIIII \ S s \ S I, \ a a I 1? m TEEI flmummsmTmmwmrnmlmmmnmmmnvmuww 3m5m Ruhr mbl hfle2 Fwflel hmh2 flflfljfifléjflflflflfléflflflflfl55fiflflfi mmmmmmnmmsmmwnnehdehhnnan 0000000050005005505000500 0 O O O O O O I o O O O O O O O O O O O O .Hhhfihdk“ ammmmmnnmnsvwnnmenmnnmssu l 11 O000000000500500000000000 can» .xmm&m.%&m“%&&w.onoulmmon%1&w.m. 0000050000000500000550000 0 O O D e O O O O O O O O O O .60 00.70th I 060 mmmmmmmmmmnmwhwmv veneems nnememnnpnmnnnspppsmmpnnn mama7mmwmnemhhwhnnnnddwnm 111 ll 0.0.0.0.0.0.0.00°00.OOKVOCSCKUOOOCOOOOOCOCOOOOOOO. 63 386 he) 33..“ mmmnnmmmennemwevv vveaeee O O O 00 0 0 0 O O O O C O O O O O O O O O MMMMW%$&MW$T2???????????? 500osooooooooosoooooooooo eseeeeeeeeeeeeeeeeeeseeee 227/0 3 3 rho/.9871 5..“3 875 2 56 89 56 8 o 3hr) 1 3h 7 mnunmllnlwzaazzz 19 TABLE II LEIGTHS (F THE ugh-Winn. VBBISSLE I (-0.5 m) Vibrissae Male 1 Male 2 Female 1 Female 2 tors n a Supercilliary , 1 140.0 ? 145.0 116.5 h6.0 ‘1 30.5 ‘I 2 37.0 37.0 2 31.0 h6.0 2 2 2 3 26.0 26.0 28.0 27.0 us .0 2 2 2 h at nf 2 16.0 nf nf nf Genal 38 .o no.0 h2 .0 1:5 .5 35.0 35 .0 nf nf Submental 1 2 2 23.0 1 .0 2 2 18.0 18.0 2 16.0 16.0 26.0 25.0 31.0 2 18.0 2 3 nf nf 23.0 2 o nf nf 18.0 18.0 Interramal nf nf nf nf R L - left nf - not found (not necessarily missing) 7 - present but damaged by removal TABLE III TIE COLOR or THE TWENTY-FIVE LCNGEST MIDTACIAL VIBRISSAE 20 ~ ~ l —~ 11.. ‘31:: Number Male 1 Male 2 Female 1 Female 2 11 g _ R .I- R 1 BBW m BBBW BBBB BBO! BBBB 38%! 2 Bill” BBBB BBW BBB? BBBB BBW BBBB 3 3880 BM BBW BBB" (BBB BBBW BWWW h W 0006 Base BBBB BBBB em BBBB 5 BBBB W m BBBB BBW BBBB BBWW 6 B31" BBBB BBBB 8383 B830 BBBB BBBB 7 was BM 38““ BBB“ BBB“ BBWW BM 8 new GM BB“! 3856 BBBW BBBB W 9 M 881315 BBBB BBBB MW BBWW B883 10 mm W BBBB BBW 3335 BB? BEN" 11 W W B333 3833 BBW (MN BBBW 12 8383 660" m M BM BBBB BBBB 1 BM 8338 BBBB $30 .38 B388 BBBB 1 BBBB OOH 8838 383‘! BBB" BBW BBBB 15 (MN W m EBBB BBBB BBW (MM 16 cm BM BBBB BBBB BBBB BBBB GM 17 88in W” BBW W (MM 8388 ‘2 18 W BBBB BBBB BBBG W BBBB BBBB 19 BB“ W W BBBB 3888 BM BBBB 20 BBBB BBBB mm W BBBB W 00“ 21 W BBW 83138 W BBBG ? GM 22 8883 case BBWW m 8836 W W 23 B“ mm W BBBB BBB“ 7 W 214 BBBW BM m BBBG BBW BBBB BBBB 25 BBW BBBW WGG W W BBBW W The letters represent the color to the nearest fourth of the vibrissal length. The first of each four letters represents the basal fourth, the last the apical fourth. The longest vibrissa is listed first, the others in decreasing order of length, the twenty-fifth being the shortest. Some fourths are banded rather than a solid color. 8 I black 0 -gmy W-white 7 - color unrecorded 21 Labiad they ‘are' reduced in length and are bordered by shorter finer white hairs. The lengths are nearly the same on the right and left sides of the same animal. Some vibrissae are paired in the follicle, but a single hair per follicle prevails s. No follicles studied con- tained more than two vibrissae. There is‘ considerable variation in length and thickness of in- dividual vibrissae when two vibrissae are found in the same follicle. In some follicles the two members» of the pair are similar in these dimen— sions. In other follicles the dimensions range from approximately the same to extreme difference in length and thickness. The colors of paired vibrissae are similar in some follicles, while in other follicles the color vario, i.e., one vibrissa is uni- formly colored while the other varies in color. The colors are shades of black or cream (called white). Table III shows that there is no apparent relationship between sex and vibrissal features. For further details concerning morphological features of m:- structure in the chinchilla consult Hana-an (19514). The integment is loosely attached to the underlying muscle which contributes to the wall of the cheek. The lining of the check is, for the most part, a mucous membrane, which appeares pale red in the fresh condition. it the rostral end there m bristle-covered pads of infolded integunent along the inner margins of the cox-enema labia oris. These modified trichm areas in delimited from the general buccal mucosa by shallow dorsoventral-linear depressions. The hairs of the cheek pad project caudad. In the case of several subgenera of woodrats studied by Howell (1926) cheek pad hairs pro- Jected in essentially the sale direction. He interpreted this arrange- sent as one in which ingress of food was ilpeded to the slightest possible dame. The lining of the cheek is pierced by the ostium of the parotid salivary gland duct , at a point opposite the anterior superior molar, and near the anterior border and ooclusal level of the molar. B. The Vestibule This restricted portion of the oral cavity is bounded by the teeth md gums internally, and by the cheeks or labia externally. There is an incisal and a solar portion. 1. The Incisal Vestibule . The incisal portion of the vestibule is located between the incisor teeth, the gingivae, and the lips. This portion is very shallow and is found around the gingivae of the incisors. It is canpletely isolated from the molar vestibule due to the fact that the upper lip forms an unbroken ring around the incisors. The shape of the loser vestibule is variable since it is dependent on both the movements and position of the labium. is the lower lip does not fuse caudal to the incisors, the circumscribed vestibule becomes continuous with the oral cavity post- incisal recess and oral cavity proper when the lobes of the inflexmn pellitum separate to admit the lingual apex. we». 4*" .'_' in. ... a“ - 23 2 . The Molar Vestibule The molar vestibule is a very narrow space located between the cheek and the molars and respective glngivae. It is circumscribed by the reflection of the buccal mucosa frm the gingivae. It is continuous with the oral cavity proper rostral and caudal to the cheek teeth row. There is no inter-molar communication with the oral cavity proper, as these teeth have no interspace. The discontinuity of the various vestibules results from the presence of a long diastema between the incisors and the molars, and also to the complex labial inflexing. c. The Poetincisal Recess The postincisal recess is the space imediately caudal to the in- cisors. It occupies the diastemal region of the mouth. Due to the labial infolding and to 'the buccal bristle pad caudal to the comissurae labia oris, it is lined with modified integument, rather than mucosa. The recess is bounded by the labia and incisors rostrally, the in- flames dorsally as well as by the incisive; papilla and hard palate. Ventrally the recess is lined withthe inflexss and lingual apex, and laterally by the buccal bristle pad. When non-distended the recess is a very minor space when compared with the oral cavity proper. It opens into the oral cavity proper at the level of the first molar teeth. Beddard (1909) found that the oral cavity of rodents was divided into two chambers by a hairy ingrowth behind the incisors. The present author refers to the first chamber as the postincisal recess, and the second, and much larger chamber as the oral cavity proper. 2h D. The Oral Cavity PrOper The cavum oris proprius (fig. 6) is directly continuous with the postincisal recess. It expands into. an inegularly ovoid chamber con- taining the molar teeth an! the tongue. Caudad the cavity is smewhat reduced; this region is the isthsus fauciun which became continuous with the pharynx. The shape of the cavity is not unifom. The molar teeth rows diverge caudally, and thus the cavity is restricted at the rostral end by the first moms, while it is much wider at the level of the last molars. The lingual fossa is somewhat irregular. The root is more regular and vaulted. The isthuus fauciun is roughly elliptical in cross section. The chief structures of the oral cavity proper consist of the palate, the floor, and sides, and in addition the molar teeth and tongue. 1. The Palate (figs. 6 and 7) The palate of the chinchilla has three well defined regions. a. The rostral region, The rostral regon continues into the postincisal recess, is an arched smooth area anterior to the first upper molars. It occupies the area of the superior diastema. Except for the superior inflexum pellitum of either side, the lining consists of a smooth moist mucous membmne. The principal structure of this portion of the palate is a fleshy pad or incisive papilla; the papilla serves as a landmark between the postincisal recess and the oral cavity proper. _ H._,.. m _.——— . 25 :98 83325 .w eggs: 38. 3.203 .ma 03.538 .p c.9333» .7305" hogan—a” .4.“ so: .0 cameo» no Mead .3 3i no 33 .m cameo» no nonsense goo—hog .2 gang 2,303” .a Bough 33933 .fi , cod canons 283 .m no.3 goagwgnflm .0." .3309.» 33.309 EH33 .N scorch . m 93305” ..n .1. cocoa .o can .353: ..m 3002 .M a on Rm .0 382$» that»: .m 3V3.» as .4 . 58: m2. 8 83a a: a: £83m omega has He 8 moaha mean an. mean a: are 2. Beds «:1. a; 8: E85 has Ea Ea. Ens gamma Eu 8 a mm... .8 EH» mam 4 .o gem 26 '1'“... \ {I'llllll , e a L oo-: 1 O \ . . . . . . . . I ... . . . . . . e .a a . . ,5? 4: $1.: \ \ \ a. \Q\\ ’0’: u: so \ \ 11$...ti.:c.::.. m \ I," \, \ l u a . b x \ o | I; a: \ \ no; I 9:. :2: .22.... \ \ \ \o I \ I a. c \ \ 5...: I: H a. 2.2.:-.: \ ...-...: ....- n: m... .......:...= 2:... 2.2:... u .9. ll at ' o I I 1 av «a 5. O "“ O “‘0 m {g ‘3 i .sl "3‘; 0r 3:2 0’ m #3;- «t. cl?" , 26 \ \ \ ......:...\=:\ \ \ \ \ ts ...... \ flu au-s¢§ \ \ \\ \\ \ \lfi" 33 em, \ \ \ . um 3.", \ \ \ \ \ \ \ \ \ \ ...... \\ o \\ \\ \\ '1’ Illllqulvc:2:::.....tm \sdulo'a \ \ \ \ \ d \ \:::.k \ \\ \ .....2... la H I ll ‘ - ’ l t I .o n l 9 . ... I: h a: a...: \ \ \ .... 1 “1. 3:2... \ ....\:a.:.: a: no ......:.==::... ......:....... I: A: ' l fi 1 I l ’1 J. .1 -' $.1- 27 FIGURE 7. A VENTRAL VIEW'OF THE PLLETE OF THE CHINCHILLA Superior incisors Inflemm pellitum superior .Median_raphe of lips Postinoisal recess Incisive papilla asooth hu-d palate (rostral region of palate) Hard palate with rugae (middle region of palate) Soft palate (caudal region of palate) Introitus pharyngeus 0stim of parotid duct Cheek Gingiva IMolar tooth SI 0v «:th - P 9,9, I U U r I c‘I" 29 The incisive papilla (figs. 6 and 7) is well developed in the chinchilla. When viewed with a dissecting lens, the papilla appears as a semicylindrical mass of tissue located in the midline just rostral to the level of the first upper molars. It is covered by the oral mucosa, and presents two ostia, one on each side of the apex of the papilla. The ostia are faintly visible to the unaided eye. The ostia lead by means of expanding channels which arch dorsad and anterad to the floor of the nasal passage. The framework of the papilla consists of cartilaginous plates at the sides of the passages. The passage seems to be lined with oral mucosa at the oral and the nasal mucosa at the dorsal end. The function of the incisive canals seems obscure in the case of the chinchilla. In various other manuals (Arey, 19116, Schour, 1953, for the lumen, Sisson and Grossman, 1953, for domestic animals, and Howell, 1926, for woodrats) the papilla and canals were associated With the organ of Jacobson or vomeronasal organ. Hill (1935) observed that the incisive foramina of rodents were elongated. Howell (1926) felt that the elongation of the incisal formina could not be due to the rather small vomeronasal nerves, but rather that the larger organ OT Jacobson was located within both of the apertures. The incisive canals were found to occupy the incisal foramina in the chinchilla. b. The middle region. The second or middle region of the palate is very firmly attached to the palatine processes of the overlying maxillary bones. This region occupies the area between the first and second molars. 30 The middle region is characterized by having transverse chevron- like palatal ridges or rugae (figs. 6 and 7). 1 minor variation was seen in the pattern of distribution of the rugae; usually four or five or more could be distinguished, the first being located slightly rostral to the first molars. The rostral and middle regions of the palate can be classified as hard palate as the bones of the skull lie in contact with them dorsad. ' c. The caudal region or soft palate (figs. 6 and 7). The caudal or posterior portion of the palate is the soft palate. This portion is limd with oral mucosa, and is very flexible and largely muscular. The back portion of the caudal division of the palate vaults the roof of the isthuus faucium ani also forms the caudal portion of the ventral wall of the nasopharynz. The front portion of the caudal division is located between the back two upper molar teeth of right and left sides. 2. The Floor (fig. 6) The floor of the mouth consists of three general divisions. The postincisal area is lined by oral mucosa and inflexes of the lips. It presents a more or less v-shaped depression for the lingual apex. The middle of the oral floor is that area between the lower molars. rhe oral mucosa lining this area reflects from the molar gingivae and from the ventral or under surface of the body of the tongue. A third or caudal portion of the floor of the mouth differs from the middle portion in that the body of the tongue gradually receeds 31 beneath the oral mucosa, thus the actual floor becomes the dorsum of the tongue and the surrounding mucosa. This third portion exhibits numerous lingufl papillae. The floor of the mouth is subtended by the mylolmoid, the geniohyoid, and digestric muscles, by various blood vessels, by certain cranial- nerve fibers, and by the various salivary glands other than the parotid, and finally by the integument on the bottom surface of the muzzle and neck. 3. The Wall of the Oral Cavity (fig. 6) The wall of the oral cavity consists of the checks. The lining of the latter is modified in the faucial region by the presence of rows of conical faucial papillae similar to the papillae of the caudal region of the dorsmn of the tongue. In addition to the papillae, the fauoes are also lined by two nearly vertical arching folds of the mucosa called the glossopalatine and the pharyngopalatine arches or pillars. Dorsally the arches are reduced in size and lose their identity in the mucosa of the soft palate. They tend to converge dorsad but never quite meet. The area between the pillars is somewhat triangular in outline with the broader base directed ventrally. The region bulges outward slightly, and with the unaided eye palatine tonsils were not discern- able . h . The Teeth The dentition of the chinchilla is a matter of much concern to the u'11C1‘t.astry, and numerous articles have been published which contain some 32 information pertaining to malocclusion and other irregular features of the teeth. Among these accounts are those of Buck (1951;), Kennedy (1952), Lindsay (1955), Peterson (1952), and Raskin (1955).. No detailed description of the teeth was found. The teeth of the chinchilla are twenty in lumber, i.e., four incisors and sixteen molars. The dental formula (Diammd method, 1952) from the time of eruption of the complete compliment of teeth was found to be 2( I § 0 g P g 14% ) 20. As the dental fonnula indicates, there are two upper and two lower incisors; they are placed in the simpliciden- tats manner. The incisors are of the glirifom, gnawing, or rodent type, 1.9., they,' did not ezdfibit true roots. Tia molars are also capable of con- tinuous eruption, as their pulp chambers likewise remain open after maturity. Their crowns are lophodont in form. According to Burt (191:6) this type of crown is cannon to herbivorous rodents. Beddard (1909) maintained that the teeth are monophyodont and that this condition is commonly found in rodents . The incisors are usually present at time of birth, but for the few neonatal specimens examined some of the molars had not yet penetrated the gingivae, although the gingivae possessed elevated areas correspond- ing to underlying molars. a. The incisors (figs. 8, 9, 10 and 13). is indicated previously, the incisors are four in number and are “ranged in a simplicidentaie fashion. They are long, strong, curved Beth, with sharp chisel-like edges. They are supported by elongated 33 FIGURE 8. Qwozpwfi'i OUTLINE DRIVINGS OF THE RIGHT INCISORS 1. Superior incisor; mesial, distal, and cross- section views, from left to right Inferior incisor; mesial, distal, and cross- section views, from left to right Position of superior and inferior incisors, from the mesial aspect Labial surface Lingual side Root end Occlusal end (apex) Mesial surface Distal surface Pulp space Esposed portion (lined diagonally) “3" w .. e V ' ' - e, 5 d-. A "' I ‘3 " L. a." l ell-J " ... . r4. ...fl 9 44 L] 0s A-J G 1.1 11 35 tubular alveolar processes of the premaxillae, and the mandibles. The major portions of the teeth are embedded or attached by a gomphosis in deep alveoli with approximately two millimeters of lingual, and eight to ten millimeters of labial exposure. The labial surfaces are pignented. The color ranges from a pale wallow in some very young animals, to a bright yellow-orange in some Mt animals. The pigmentation did not extend below the alveolar ridges more than a millimeter in the specimens examined. Schour (1953) indicated that this piynent was contained in the outer portion of the dentine in the rat incisors. The dentine of rodent incisors generally contains two layers, the outer constituting about one-fifth the thickness of the dentine (Watson and Avery, 195,4). No comment was made concerning the nature of the pigment. Attempts to remove the pignent from the ch:thmchilla incisors indicated that the pigment was not merely a surface £111., The rate of growth of chinchilla incisors was studied by others. K01Inedy (1952) observed that the average ammal rate of growth was 2.31: inches for the uppers, and 3.16 inches for the lower incisors. Thus “'3 rate of wear about equals the rate of growth. According to these figures and also on the basis of observations made in this study, the substance of the incisors will be replaced at least three times a year. Compared to the data by Schour (1953), for the rat, which indicated that the tooth substance is replaced every forty to fifty days, the rate of 1mriser growth in the chinchilla is relatively slower. 36 The upper or premaxillary incisors (figs. 3, "6, 8 and 9) are sharply curved, and almost form a complete semicircle. The length of the greater curvature (labial surface) is approximately 20 m., while the length of the lesser curvature is approximately 13 an . The diameters of the teeth ”‘9 nearly the same , although somewhat greater in a labial-lingual direction (2 mm) than in a mesio—distal direction (1.9 mm). The occlusal plane slopes at an acute angle to the cutting edge. On this sci-race a distinct transverse ledge was ustnlly present, and a'IJ‘Parently represented the point of greatest wear by occlusion with the 133.31“). edge of the lower incisors. The proximal or embedded end of the upper incisor remains widely Open, the well being a thin shell. The rim of the shell on extracted teeth of skeletal preparations - aI’Dears serrated or irregular and tissue-paper thin. The pulp chamber 01' the root is nearly as wide as the diameter of the tooth, and gradually becomes narrower and nearly displaced with tooth substance at about two- thirds the distance toward the occlusal or distal and (11g. 8). From this level occlusiad a capillary-like canal proceeds; its caliber be(names too well to trace grossly at a point somewhat below the occlusal 3\ll't'ace. The proximal and rests in a rounded aninence at the junction of the PPGInuillary and maxillary bones, and is thus partially contained by bOth bones. The suture indicated lies about rive millimeters rostrad of the anterior root of the £180“. The ordnance over the apex toms the I'OStral and inferior margin of an extensive preorbital roses on the literal surface of bones of the face. r. V- w— 37 FIGJRB 9. FIGIRE 10. LLATERLL VIEW OFTKE SULLVITHTHEMANDIBLEREQOVED AND THE EMBEDDED PORTIONS OF THE TEETH OUTLINED Bamymoaz Incisar Incinl emineme of premufllu'y bone Premuillary bone Nasal bone Maxillary bone Orbit. Frontal bone Zygomatic arch Parietal bone Tympaxm: bulla Occipital bone THEHHDIAL WEEWRIGHTM WTHEHANDIBIEWI’IH THE 313mm PORTION: OF TEETH GITLINED AND THE Pam END (F TE INCISOR W wagH Incisor Mandibular process mam Rm Coronaid Condyle Angular Pterygoid spine Gr _ /vw.. . . . » KfuLuw Ly \ I . H‘Y 1) ‘Lxr‘ \- x.“ 1m , i» , y a: . . A .. .. .\ Aria/:1 . .K .5 ,U "% . .. J. .... f _ .. .. ,y , 81’ CT ‘1' I? 39 The lower incisors (figs. 3, 6, 8 and 10) resemble the upper incis- 01'3 in form and structure. They appear much longer than the upper teeth because of a much lesser degree of curvatun. By measznement they are Only a few miJJimeters shorter, end to end. The pulp chamber remains Widely open for a relatively greater length of the tooth (fig. 8) . The dil-lllsters of the lower incisors are nearly the same as the diameters of the uppers. Il'he teeth are somewhat tlticker than wide. The occlusal surfaces of the lover incisdrs slope away from the labialoocclusal angles as in the upper teeth, but bear no distinct ledges. The temporOmandibular articulation is such that it permits a forum-backward movement of the mandible . The lower incisor can thus 8trike the occlusal surface of the upper, or it's occlusal surface can strike the incisal edge of the upper incisor. The upper and lower incisors are thus both kept sharpened in a chisel shape by the action of the opposing teeth. The proximal portion of the mandibular incisors rest internal or medial to the cheek teeth or molar roots. The edge or base margin lies °PPOsite the second and third intennolar space (fig. 9). Both the upper md lower incisors are deeply and firmly embedded, making them difficult to extract in fresh specimens without damaging other tissues. When the incisors occlude the opposing molars are held apart by a wow gap, due to the great length of the incisors. In addition the 1°‘Uer molars now shift forward in respect to the opposing upper molars, “O that the last two molars lie inferior to the first two upper molars. The incisors and molars can thus not be in occlusion simultaneously. ho b. The molars or cheek teeth (figs. 6, 9, 10, 11 and 12) - The molars or cheek teeth total sixteenin number, 1.6., four molars in each quadrant of the jaws. The molars are separated from the incisors by a long endentulous diastema, which is nearly as long as the cheek teeth rows imediately caudad. The molars are monophyodout and possess lophodont crowns. Since the proximal ends remain open these teeth are classified as a continuous growth and eruption type. Reports on the rate of eruption and attrition of chinchilla molars were not found in the literature. The morphological features of all the chinchilla molars are essen- tially alike. In outline they appear as square columns with rounded fingles, an! are roughly three times as high as wide. Each molar possesses it mesiodistsl and a buccolingual curvature. The occlusal surfaces of the lower molars are somewhat more angular in outline than the correspond- ing surfaces of the upper molars. Though each molar appeared to be a Sclid block, close inspection revealed that each is canposed of three a<>llaewhat unequal fused sub-units, although fusion of the units was not completed proximally. Due to the nature of the different shapes of the Bub-units, and to the way in which fusion of units occurred, three POI‘tions were visible on the lingual surface of the mandibular molars, "1‘3 on the buccal surface of the maxillary molars. Only two of the three portions were apparent on the opposite surfaces of these teeth (figs. 11 and 12). As all of the molars are of the continuously erupting type, they do “”3 have roots in the usual sense of the word (Sisson and Grosanan 1953). That portion which corresponds to the root in other teeth is referred to as the basal portion or proximal end by Schour (1953). Other than for the extreme proximal tip the teeth are quite 8131110 in structure arm! in outline for their entire lengths. Thus, cram, neck, cingulum, and root do not exist as entities in chinchilla molars. The molar con- sists of an outer covering of cementm, a thin enamel layer, and an inner dentine adjacent to the pulp chamber. The latter is obliterated by dentine near the occlusal extremity The first lower molar is more triangular in outline than the other lover molars; the last or fourth upper molar is somewhat avoid in out- line as compared with the preceding three molars. Two curvatures along the long axis of the molars are striking features of these teeth, but they do not become obvious until the teeth are removed frm or are exposed in their alveoli. Viewed laterallyifig. 13) when apposed, the upper and lower cheek teeth contribute equally to a sigmoid curve. The convexities of the upper molars are mesiad, and in the lower molars distad. Viewed frontally (figs. 11: and 18) the opposing upper am lower I"Glare are arranged in a continuous are, with the convexity directed toward tdue lingual surface. Because of the lingual-buccal curvature, the bottoms 01’ the teeth do not lie at right angles to the long axis nor in a horizontal plans when the head is level, and hence are not directed downward or upward in the respective jaws. The basal surfaces of the maxillary molars are directed sidewise at ‘bout forty-five degrees to the horizontal. Thus they face the orbit. ’ ‘T'BL 1:2 FIGURE 11. DRAWINGS or THE occmsu, HESIAL, DISTLL, moon. um HNLMAL SJRFLCES (F THE RIGHT HANDMLAR nouns - 1. First molar B. Second molar C. Third molar D. Fourth molar O. Occlusal surface (8!) H. Mesial surface (3!) DI. Distal surface (31) BU. moon surface (3:) L. Lingual surface (31) E. filamel ridge DE. Dentine CE. Cementum Note : Heasm-ements for the mandibular right molars illustrated in this plate are listed in Table IV. i 9 I 33,03 '7‘ 2-. .IilJIII. . lift? f Jig}: 1! I1 .I. TABLE IV WSINWEBSOEHOIABS ILLUSTRATED] FIGURES 11 AND 12 Mandibular Mesiodistal Buccolingual Length Right Molar 1 3.0 3.0 9.6 2 3.0 3.1 9.5 3 2.5 3 .o 10.0 h 2.0 3.0 8.5 Maxillary Right Molar 1 3.0 3.5 9.9 2 3 .0 3.5 9.8 3 3.0 3.5 8.9 h 3 .5 3 .0 7 .9 LS FIGJRE 12. DRAWEGS OF THE OCCLUSAL, MESLLL, DISTAL, BUCCAL, AND LINGJAL SJRFACES OF THE RIGHT WAR! MOLARS 1. First molar E. Second molar C. Third molar D . Fourth molar O. Occlusal surface (81) M. Hesial surface (31) DI. Distal surface (31:) BU. Buccal surface (31) L. Lingual surface (31) E . Enamel ridge DE . Dentine CE. Cementum Note 3 Measurements for the maxillary right molars illustrated in this plate are listed in Table IV. t 116 1; (III‘ILJ‘? ’ . . "ll/III. ’ o ' B g’llllifllt'é 08 33 116 A '5 -. --. \IIIIIIIII’ _ Ill/1f” h? FIGJRE 13. Note: FIGJRB 1h. FIGJRE 15. 1 SIDE VIEW OF THE SKULL SEWING THE CURVATURE OF THE MOLARS AND THE POSITION (1" THE INCISORS WHEN THE RESPETIVE MOLLRS (ECLUDE .1. B. C. D. E. Incisor Molars Mandible Manlla Premaxilla The zygomatio arch has been removed , and the caudal portion of the skull is not shown. A FRONTAL VIEW 0' THE UPPER 1N1) LOWE JAWS (HOWE) Sill-INC: THE LATHE. CURVITURE (F THE MOLlRS AND THE RELATIVE POSITION (1" THE BASIL OR BUFTCH PLANES CF THE MOLLRS 1. B. C. D. E. F. Nasal Passage Maxilla Upper Molar Lower Molar Mandible Position of root of mandibular incisor A DEW Q“ THE MANNER (1" (ECU) SIGN OF THE VARIWS MOI-LR TEETH I, II, III and IV - Upper Molars l, 2, 3 andh - LomrMolars 119 There is no expanded maxillary antrum above the teeth, and the medial wall of the orbit 15 partly formed by the lateral plate of the alveolar process of the maxilla, against the inner side of which rests the basal planes or bottom of the upper molars. The bottom surfaces or basal planes of the lower molars face almost directly laterad against the lateral wall of the body of the mandible, and hence lie at nearly a right angle to the long axis of the teeth. The basal planes are also the nearly vertical in the level head. The alveoli of the various cheek teeth are incomplete in that there is no boww partition between the occlusal two thirds or more of adjacent molars. There is a vertical inner-molar ridge along the walls of the alveoli opposite the line of contact of each two molars . hen though the molars are quite similar in shape and dimensions, the bony ridges prevent the interchange of teeth front socket to socket. is the inter-molar Septum is incomplete, there is no interspace between the molars for most of their length. When the mandible is fully retracted the upper molars occlude with their respective lower molars. Subsequent to maximum retraction of the mdimdible, occlusion is not perfect, since the upper molars are more ‘fidely separated than the lower molars (figs. 11; and 15) . Further, a; the width of the upper and lower molars is approximately the same, the lateral edges of the occlusal surfaces of the upper molars project beyond the lateral surfaces of the lower molars. If the lateral and -“ x"Radial surfaces of the upper and lower molars of one side are aligned, 50 the upper molars of the apposite side overhang the lower teeth by almost one half their width. when the lower incisors strike the occlusal slaps of the upper molars, the mandible is shifted entered to the extent that the first lower cheek teeth lie rostrad to the first upper molars. When the lower incisors are shifted still more anterad so that the incisal edges of the upper incisors strike the occlusal surfaces of the lower incisors, both the first and second lower molars are rostrad to the first two upper molars . When the incisors occlude in either relationship, the Opposing upper ani lower molars of either side are separated by a gap of a millimeter or more, and hence do not occlude. The occlusal surfaces of the molars are rough planes. When occlusion is achieved the opposing planes meet in a slanted, rather than a horizontal plane, i.e., they slant domward from buccal to lingual. Prominent ridges of enamel on the occlusal surface outline the sub- divisions of each tooth. External to the enamel is a narrow covering of cementum, and internal to the enamel are central areas of dentine. The latter two substances are irregularly worn, so that between the enamel ridges depressions are fomed in which the enamel ridges of the oppos- ing teeth rest. For any one upper molar the rostral enamel ridge of the three subdivisions is less worn than the caudal ridge; for the lower 1"03.3.). the caudal enamel ridges of the subdivisions are less worn than ‘I‘e the rostral. The central dentine areas exhibit depressions. When these regions are observed by means of a dissecting microscope (magnification 3X) the 51 depressions are found to be rough transverse grooves. Emimtion of the drawings of the occlusal surfaces of the molars reveals (figs. 11 and 12) that the transverse. ridges of the opposing upper and lower molars are 'variabls, i.e., the ridges in the former es. directed transversely and in the latter obliquely. For further details concerning dimensions of upper ani lower molars see Table IV. The teeth appear to be well adapted to a herbivorous diet. For a short tine after birth, each molar consists of three adherent portions and enamel ridges are not observed. By maturity the individual units are fused and the apices are worn any. The enamel becomes; a: reduced that only the outer portion around the cones remains as ridges, and the dentine is exposed centrally. s. The Tangle (figs. 6, 16, 17, 18 and 19) Literature dealing with the chinchilla tongue is fragmentary. Kennedy (1952) indicated that the actions of the tongue are sometimes hindered by malocclusion of the molars. The tongue is a long slender highly muscular organ. 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