THE MECROSCOPIC ANATOMY OF THE ENTEGUMENT 0F MATURE FEMALE AND MATURE CASTRATED MALE YQRKSHIRE H065 Wash For fin Dogma af’ M. 3. MiCHiGAN STATE UNWERSITY Heron? Q. Mar'carian i962 3142295 LIBRARY Michigan State 2 University THE MICROSCOPIC ANATOMY OF THE INTEGUMENT OF MATURE FEMALE AND MATURE CASTRATED MALE YORKSHIRE HOGS BY Heront Qo Marcarian A THESIS Submitted to Michigan State University In partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Anatomy 1962 To CLO It is the hope of the author that the following passage by Edgar Guest will be as much help to the reader as it was to him. When things go wrong as they sometimes will, And the road you're trudging seems all uphill. When the funds are low and the debts are high, And you want to smile but you have to sigh. When care is pressing you down a bit, Rest if you must — but don't you quit. Success is failure turned inside out, The silver tint of the clouds of doubt. And you can It may be So stick to It's when never tell how close you are, near when it seems afar. the fight when you're hardest hit, things seem worst that you mustn't quit. - Edgar A. Guest - iii ACKNOWLEDGEMENT S Thousands of words are incorporated into a book, however not one of them may stand alone and have meaning. The author of this manuscript is likened to a single word. Without the gracious assistance of friends, associates and teachers this manuscript would have been as imaginary as a one word novel. Sincere appreciation and thanks are extended to Dr. M. Lois Calhoun, Professor and Head of the Department of Anat- omy, for her guidance, encouragement, and consideration dur- ing the course of this investigation. Gratitude is expressed to Drs. Madan B. Bharadwaj, Roger Brown and Esther M. Smith for their criticisms of this manuscript. Special thanks are extended to Dr. J. Thomas Bell for timely advice and suggestions, to Mrs. Esther Colby for technical assistance and training, and to Dr. James H. Stewart for his assistance in the acquisition of the animals used in this study. Thanks are also due to Miss Lisa Neu, Bacteriology technician, for the use of laboratory equipment, and to the staff of the Michigan State University slaughter house for their assis- tance in collecting the skin specimens. iv TABLE OF CONTENTS Page INTRODUCTION . . . . . . . . . . . . . . . . . . . . 1 REVIEW OF THE LITERATURE . . . . . . . . . . . . . . 3 Epidermis . . . . . . . . . . . . . . . . . . . 4 Dermis . . . . . . . . . . . . . . . . . . . . 9 Hair . . . . . . . . . . . . . . . . . . . . . ll Sebaceous Glands . . . . . . . . . . . . . . . . 13 Sweat Glands . . . . . . . . . . . . . . . . . . l4 Carpal Glands . . . . . . . . . . . . . . . . . 15 MATERIALS AND METHODS . . . . . . . . . . . . . . . 16 RESULTS AND DISCUSSION . . . . . . . . . . . . . . . 26 Skin Thickness . . . . . . . . . . . . . . . . . 26 Epidermis . . . . . . . . . . . . . . . . . . . 27 Dermis . . . . . . . . . . . . . . . . . . . . 30 Hair . . . . . . . . . . . . . . . . . . . . . . 33 Sebaceous Glands . . . . . . . . . . . . . . . . 36 Sweat Glands . . . . . . . . . . . . . . . . . . 37 Carpal Glands . . . . . . . . . . . . . . . . . 38 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . 39 LITERATURE CITED . . . . . . . . . . . . . . . . . . 43 Table LIST OF TABLES Measurements of epidermal, dermal, total skin thicknesses of male 1 . Measurements of epidermal, dermal, total skin thicknesses of male 2 . Measurements of epidermal, dermal, total skin thicknesses of male 3 . Measurements of epidermal, dermal, total skin thicknesses of female 1 Measurements of epidermal, dermal, total skin thicknesses of female 2 Measurements of epidermal, dermal, total skin thicknesses of female 3 vi and Page 20 21 22 23 24 25 Plate II. III. IV. VI. VII. VIII. IX. LIST OF PLATES Page Body areas from which skin specimens were taken . . . . . . . . . . . . . . . . . 18 Cellular stratum corneum with nuclear remnants--vertical section of the snout . . 48 Individual arrangement of tactile hairs—- horizontal section of the lip . . . . . . . 50 The innervation of a single tactile hair-- horizontal section of the lip . . . . . . . 52 Elastic fibers in the trabecula of a tactile hair—~horizontal section of the lip . . . . . . . . . . . . . . . . . . 54 The hair pattern showing characteristic triads and two hairs in a single follicle—— horizontal section of the bridge of the nose . . . . . . . . . . . . . . . . . . . 56 The hair pattern showing triads and groups of two--horizontal section of the medial carpus . . . . . . . . . . . . . . . . . . . 58 A triad in which the hairs are the same relative size--horizontal section of the lateral brachium . . . . . . . . . . . . . . 60 A single arrector pili muscle attached to two hair follicles-—horizontal section of the dorsal sacrum . . . . . . . . 62 A single hair follicle with two arrector pili muscles--horizontal section of the dorsal thoraco-lumbar area . . . . . . . . . 64 vii Plate XI. XII. XIII. XIV. XVI. XVII. XVIII. XIX. Page Follicular folds with surrounding sebaceous glands--vertical section of the bridge of the nose . . . . . . . . . . . 66 Follicular folds--vertical section of the bridge of the nose . . . . . . . . . . . 68 Follicular fold—like structures at the bulb of a hair follicle--vertical section of the upper eyelid . . . . . . . . 70 Two hairs in a single follicle-- vertical section of the upper eyelid . . . . 72 Arrangement of the dermal fibers showing the papillary and reticular layers-- vertical section of the lateral thorax . . . 74 Elastic fibers in the dermal papilla of a hair follicle—-vertical section of the bridge of the nose . . . . . . . . . . . . . 76 An arrectores pilorum muscle attached to the bulge of the outer epithelial root sheath—-horizontal section of the prepuce . . . . . . . . . . . . . . . . . . 78 Epidermal projections of the interdigital skin--vertical section . . . . . . . . . . . 8O Mast cells and eosinophils in the reticular layer of the dermis—-horizontal section of the ventral abdomen . . . . . . . 82 Elastic fibers of the cartilage projected into the adjacent dermis—-vertical section of the external ear . . . . . . . . . . . . 84 The arrangement of sebaceous glands around ‘the hair follicles--vertical section of the upper eyelid . . . . . . . . . . . . . . . . 86 viii Plate XXII. XXIII. XXIV. Page Ducts of the sebaceous gland opened into the hair follicle——vertical section of the upper eyelid . . . . . . . . . 88 Resting phase of the apocrine sweat glands-~horizontal section of the dorsal sacrum . . . . . . . . . . . . . . . . 90 An apocrine sweat gland in the secretory phase--vertical section of the dorsal sacrum . . . . . . . . . . . . . . . . . . . 92 ix INTRODUCTION An abundance of information concerning human skin has been presented by Montagna (1956), Dick (1947), Pease (1951) and others. Unfortunately, the dermatology of domestic ani- mals has been neglected. A series of studies on the integu- ment of domestic animals in the Department of Anatomy at Michigan State University has done much to relieve this sit- uation, namely, Webb and Calhoun (1954) dog; Goldsberry and Calhoun (1955) cattle; Strickland (1958) cat; Smith (1960) newborn swine; Holmes (1960) rat; and Fowler (1962) fetal pig. Swine dermatology in particular has been neglected by histologists. Since hogs are a source of food and clothing necessary to our economy, an understanding of the normal histology of swine integument is important in diagnosing pathological conditions. The purpose of this paper is to present the results of the histological study of the skin of mature female and mature castrated male hogs. The anatomy of the skin of both sexes will be discussed simultaneously, however struc- tural differences between the sexes will be noted whenever present. References will be made to the skin of other domestic animals and to man for comparison. It is the hope of the author that this paper will serve as a useful reference for investigators requiring knowledge of normal swine histology. REVIEW OF LITERATURE A careful search of the literature has revealed very little information concerning the skin of swine. Most of the work on skin, of which Montagna (1956) has done con- siderable, has been devoted to the study of the human inte- gument. Investigations of the latter include, the dermo- epidermal junction by Szodoray (1931), Dick (1947), Baum- berger gt a1. (1942), Odland (1950) and Katzberg (1958); innervation by Woolard (1936), Weddel (1941), Montagna and Ellis (1952) and Winkelman (1959); electron microscope studies by Adolph §;_§l. (1951), Pease (1951), Gray £3 a1. (1952), Hibbs and Wallace (1958) and the histology of hair byLeblond (1951). Montagna and Ellis (1952) have devoted an entire book to the biology of hair and hair growth. Pertinent references to the skin of domestic animals follow: Goldsberry and Calhoun (1955) and Findlay and Jenkinson (1960) cattle; Cooper and Franklin (1940), Andrew and Andrew (1949) and Holmes (1960) rat; Strickland (1958) cat; webb and Calhoun (1954) mongrel dog; Billingham and Medawar (1947) guinea pig; Takagi and Tagawa (1961) horse; and Dixon (1961) rat, rabbit, cat and monkey. The best information to date concerning the skin of swine was found in books by Ellenberger (1906), Wilson (1941), Sisson and Grossman (1956) and Trautmann and Fiebiger (1957). The earliest study of swine integument was made by Flatten (1896). David (1932) made a histological study of Mexican hairless swine skin (Sus scrofa). Smith (1960) and Fowler (1962) reported on the histology of newborn swine and fetal pig respectively. Special studies on swine skin in— clude, the inheritance of hair whorles by Craft (1932), the histology of wattles by Roberts and Morrill (1944), a report on thermal injury to swine skin by Moritz and Henriques (1947), the vibrissae of Sue scrofa by Moriconi (1953), and an electron microscopic study on the cells of the pigs car- pal organ by Kurosum and Kitamuro (1958). Irving (1956) classified swine as bare skinned animals and studied their physiological insulation. Epidermis The epidermis, which is the most superficial layer of the skin, is composed entirely of stratified squamous epi- thelium. The epidermis is sometimes called the cuticle, as it is the outermost covering of the skin (Dawson, 1948). Histologists generally subdivide the epidermis into four distinct layers; Stratum corneum Stratum lucidum Stratum granulosum Stratum germinativum Ham and Leeson (1961) further subdivided the stratum ger— minativum into the stratum spinosum or prickle cell layer and the stratum cylindricum or the basal cell layer. Golds- berry and Calhoun (1955) reported that in the skin of Here— ford and Aberdeen Angus cattle, in most instances, only two clearly defined subdivisions of the epidermis were present-- the stratum corneum and stratum germinativum. The stratum corneum is composed of dead, clear, keratin- ized cells. The most peripheral cells of this layer, the stratum disjunctum, consist of dried, horny plates which are constantly being desquamated (Dawson, 1948). Pease (1951), in a study of human epidermis, observed that the stratum corneum was arranged in cuticular plates, the lat- ter being held together by remnants of the intercellular bridges. Keratin is thought to be formed from tonofibrils (Leblond, 1951). Histologists generally agree that the stratum corneum, in human skin, is thickest on the palms and soles. The stratum lucidum is not evident in most sections of human skin. The cells of the stratum lucidum are filled with a semifluid, eleiden, which is believed to be a trans— formation product of keratohyalin granules (Ham and Leeson, 1961). Smith (1960) and Fowler (1962) in their respective studies of new born and fetal swine did not observe this clear layer. webb and Calhoun (1954) reported a stratum lucidum in most sections of mongrel dog integument. The cells of the stratum granulosum contain character- istic keratohyalin granules. Montagna and Ellis (1952) reported a decrease in the number of mitochrondria and Golgi elements in cells possessing these granules. The epidermal cells begin to degenerate in the stratum granulosum (Ham and Leeson, 1961). The cells of the stratum spinosum are characterized by well defined intercellular bridges projected from their sur— faces. According to Odland (1958), 40 to 50 intercellular bridges may be present on a single cell of the stratum spino— sum. The cell membrane of a prickle cell,which may be a dou- ble membrane does not possess a supporting structure for the projected intercellular bridges (Pease,l951). The intercellu- lar bridges of adjacent cells make contact with each other, but there is no protoplasmic continuity through this bridge (Copenhaver and Johnson, 1958). A pair of attachment plaques, one from each bridge, forms a thickening at their point of contact called a desmosome (Odland, 1958). Between these two plaques, a thin dense lamina serves as the point of attachment between the two adjacent intercellular bridges. Odland (1958) further reported that bundles of intercellular filaments (tonofibrils) converge near the attachment plaques and appear to be attached to the internal faces of these plaques without passing from one cell to another. Adolph _§_§l, (1951) noted that the precipitated cytoplasm of these cells exhibit a fine feltwork of fibrils which are of a different size than the tonofibrils. These fibrils are laid down in a random manner and have no apparent relation to the intercellular bridges. The stratum cylindricum (basal cell layer) rests on the basement membrane and its cells proliferate and push up into the stratum spinosum. Cowdry and Thompson (1944) found max- imum cell division in the basal layer, however they further reported the level of mitosis in the epidermis is not fixed but subject to change in different physiological conditions. A diurnal rhythm exists in the frequency of mitosis in the epidermis of mice ears, a gradual increase to a maximum at 10 A.M. and a decrease to a minimum at 10 P.M. (Cooper and Franklin, 1940). Andrew and Andrew (1949) observed lympho- cytes are always present in the normal epidermis of rat and man. They constitute about 1 to 4% of the cells in the stratum germinativum and are located primarily in the basal layer. These same authors theorized that the lymphocytes become recognizable as clear cells, and by differentiation of the cytoplasm are transformed into ordinary epithelial cells. According to Hibbs and Wallace (1958), the cyto- plasmic membranes of the basal cells and cells of the stratum granulosum were smooth, while those of the stratum spinosum were sharply scalloped. There has been much speculation and contradiction con- cerning the attachment of the dermis to the epidermis. At one time or another, reticular, collagenous and elastic fibers have been thought to bridge this dermo-epidermal junction. Baumberger gt a1. (1942) observed binding mate- rial between the dermis and epidermis exhibiting physical properties corresponding to those of collagen and therefore concluded that collagenous fibers are cemented to basal cells, presumably by an amorphous material. Dick (1947) found reticular fibers bridging this dermo-epidermal junction. Odland (1950) reported the cytoplasmic processes of basal epidermal cells inserted into the spaces of a continuous meshwork of dermal reticulum. Pease (1951) stated that the basal layer in some regions is characterized by heavy gelatinous cords (Herxheimer fibers) which are thought to connect the dermis and epidermis. The area of the dermo-epidermal junction has been thought to decrease with age. This decrease is believed to be brought about by the collapse of the dermal papillae as the involution of the vascular structures precipitates metabolic deficiencies in the dermis (Katzberg, 1958). Dermis The dermis, which lies directly beneath the epidermis, is divided into two layers blending into each other without a distinct demarcation-—the superficial or papillary layer and the deeper reticular layer. Wilson (1941) referred to the superficial layer as the thermostat layer, however this term is not in common use. Histologists agree the papillary layer is composed of delicate collagenous, elastic and reticular fibers having a loose arrangement. According to Wilson (1941), elastic 10 fibers are more abundant in the papillary layer of swine integument than in the reticular layer. The elastic tis— sue of normal human skin consists of a superficial sub— epidermal network of fine fibrils and a deeper layer of large fibers (Dick, 1947). Elastic fibers are more numer- ous in human than porcine dermis (Moritz and Henriques, 1947). The papillary layer has numerous capillary meshes and lymphatics. A plexus of lymphatic capillaries origi- nates in the dermal papillae. The reticular layer is com? posed of coarse collagenous fiber bundles situated parallel to the surface of the skin. Wilson (1941) reported hog skin differs from that of other domestic animals by possessing a reticular layer composed almost entirely of adipose tis- sue. He further stated castration gives a smoother and more uniform structure to the skin of domestic animals, the skin becoming tighter and more dense after castration. The skin in vivo is a gel, in part composed of macromolecules, which become the elastic fibers noted in fixed tissues. Because the skin itself is elastic, the fibers may act as tightening agents of the skin (Jarrett, 1958). The dermis of swine skin possesses a superficial and deep vascular supply. The sebaceous glands and epithelium 11 are supplied by the superficial vascular plexus and the sweat glands derive their vascularity from the deeper plexus (Wilson, 1941). Hair The hair follicle is an epithelial structure surrounded by a connective tissue sheath. A bundle of smooth muscle fibers, the arrector pili muscle, is attached to the top connective tissue sheath about half way down the follicle.- The arrector pili muscles of the hog average 40 microns, this being thicker than those of most domestic animals (Ellenberger, 1906). The arrector pili muscles are con- spicuously thick in the sheep and often double in the pig, however they are thin on the bristles of the pig (Trautmann and Fiebiger, 1957). There is a great diversity of hair patterns among mam- mals. The hair of the pig, dog, and cat occur in groups (Trautmann and Fiebiger, 1957). According to Flatten (1896) and Smith (1960) the hair of swine is usually arranged in groups of three. Flatten (1896) further reported the mid— dle hair of the triad to be larger and extended deeper into the dermis. Norback (1951), in his study of hair, reported 12 that Hofliger (1931) observed secondary hair follicles of sheep and hogs, which in some cases, were similar in size to the central primary follicle. webb and Calhoun (1954) stated the hair follicles in mongrel dogs occurred in groups of three, there being up to twenty hairs in a single group. The hair of newborn swine was generally found in groups of three, with only one hair per follicle regardless of the size of the hair (Smith, 1960). Fowler (1962) occasionally observed two hairs in a single follicle. Strickland (1958) reported 12 to 20 hairs diverging from a single follicle in the skin of cats. Holmes (1960) observed the general body hair of the rat to be arranged in well defined groups of follicles, the central follicles appearing in linear form but alternating position from row to row, producing a cobble- stone appearance. David (1932) discovered normal hair folli- cles in the skin of the Mexican hairless swine, but they extended in abnormal directions under the epidermis and the hairs were not evident on the body surface. Goldsberry and Calhoun (1955), in a study of the inte— gument of cattle, observed ”follicular folds” which consis— ted of 7 to 20 folds below the opening of the sebaceous glands and projected into the lumen of the follicle. These 13 folds were also reported by Strickland (1958) cat; Holmes (1960) rat; Smith (1960) newborn swine; and Fowler (1962) fetal pig. Montagna (1956), who called these folds "corru— gations," reported their presence in rats, sheep and mice, but stated they were not present in man. Many mammals possess sensory hairs. Winkelman (1959) differentiated sensory hair from common hair by the degree of development of the individual components and the presence of a connective tissue capsule which enclosed the sinus of the sensory hairs. He further reported the sensory hair is innervated by 2 to 5 large nerve trunks penetrating the connective tissue capsule at its base. Dixon (1961) noted vibrissal hairs were innervated by extremely thick nerve bundles passing obliquely through the connective tis- sue capsule at its base and spread through the epithelial root sheath of the follicle. Tactile sinus hairs have never been demonstrated in the human species (Montagna and Ellis, 1952). Sebaceous Glands Sebaceous glands are epidermal appendages developing from the side of the hair follicle which makes an obtuse 14 angle with the surface with the skin. The cat and pig have apocrine glands in the ear canal similar to those of the human species (Baumann ££.§1~: 1958). According to Trautmann and Fiebiger (1957), sebaceous glands are rudi- mentary in the pig, and Sisson and Grossman (1956) reported the sebaceous glands of the pig were small and less numer- ous than those of other domestic animals. Smith (1960) observed six sebaceous glands surrounding each tactile hair follicle. Montagna and Ellis (1952) stated the nuclei of the cells in the central part of the gland are pyknotic in man. Sweat Glands The sweat glands of the pig, as in most domestic ani- mals, are apocrine (Trautmann and Fiebiger, 1957). Moritz and Henriques (1947) observed glands in the dermis of the pig which had some resemblance to the sudoriferous glands of human skin, however they were nonfunctional. According to Trautmann and Fiebiger (1957), the secretory tubule is glomiform in the pig. The apparent size of sweat glands may vary depending on whether the skin is obtained from slaughtered or biopsied animals, being larger in the latter 15 (Findlay and Jenkinson, 1960). Hurley and Shelley (1954) stated the role of myoepithelium in the human apocrine. sweat gland was primarily of contraction. Furthermore,they reported these contractions occurred in peristaltic waves with a definite refractory period and theorized the apo- crine tubules served as a reservoir for apocrine sweat. Carpal Glands Trautmann and Fiebiger (1957) reported the carpal glands of the pig comprised 1 to 12 cutaneous invagina— tions which contained greatly branched, brownish merocrine mucous glands with many smooth muscle fibers. The carpal gland of the pig is a conglomerated sweat gland, histolog- ically similar to the smaller eccrine gland of man (Kuro— sum and Kitamuro, 1958). Flatten (1896) noted carpal glands on the medial skin of the carpal joint. He further reported these glomiform glands, present in the reticular layer, flow into "superficial tubules of the dermis." MATE RI ALS AND ME THODS Source of Animals The animals used in this investigation were obtained from the Michigan State University slaughter house, and passed ante and postmortem inspection by a federal veterin— arian. Three sexually mature female and three mature cas— trated male hogs were studied, ranging in age from six months to one year and weighing approximately two hundred and fifty to three hundred and fifty pounds. Technique Immediately upon slaughtering, skin specimens were obtained from twenty one body areas (Plate I) and placed in a mixture of commercial formalin, 95% ethyl alcohol, gla— cial acetic acid, and distilled water (Lavdowsky's mixture, Guyer, 1949). The tissues were removed from this mixture after approximately fifty hours and stored in 70% alcohol. The specimens were dehydrated and infiltrated by the butyl-alcohol-mush method of Johnson, §£_a1. (1943). The tissues were embedded in "Tissuemat” and horizontal and vertical sections were cut, 7 to 9 microns, and stained with Harris' hematoxylin and eosin, weigert's and Van Gieson's 16 l7 connective tissue stain, Mallory's Triple Stain (Crossmon's modification, 1937) and Giemsa's stain. Slaughtering pro- cedures prevented the acquisition of skin specimens from the hind limb, therefore the latter area was not included in this study. Measurements Epidermal and dermal thickness was measured with an ocular micrometer and recorded in microns. Every figure. represents an average of six measurements. Density of mast cells and elastic fibers were estimated qualitatively. The size of sweat glands was based upon a comparative deter- mination, only the largest and smallest being noted, since true cross sections could not be determined. A. Head (a) (b) (C) (d) (e) (f) B. Thor PLATE I 18 Body areas from which skin specimens were taken Lip - upper . . . . . Snout . . . . . . Bridge of nose . . . Eyelid - upper . . . External ear . . . . Neck - dorsal . . . ax (a) Dorsal thoraco - lumbar (b) Lateral thorax . . . (c) Ventral thorax . . . C. Trunk (a) (b) (c) (d) (e) (f) (g) D. Fore (a) (b) (C) (d) (e) Dorsal sacrum . . . . Lateral abdomen . . . Ventral abdomen . . . Prepuce . . . . . . . Tail . . . . . . . . Anus . . . . . Vulva . . . limb Lateral brachium . . Axilla . . . . . . . Lateral carpal region Medial carpal region Interdigital skin . . Section No. O‘UWQLUNH 13 18 12 20 19 10 11 14 15 16 17 21 TABLE 1 MEASUREMENTS OF EPIDERMAL, DERMAL, AND TOTAL SKIN THICKNESSES (Male 1) EPIDERMIS DERMIS TS AREA RANGE* A RANGE A E+D Lip 146-234 173 873-1042 983 1156 Snout 231-348 286 2241-3007 2878 3165 Bridge of nose 127-182 159 1423—1749 1514 1673 Eyelid 60-136 91 Ear 62-118 91 547- 858 786 877 Dorsal neck 149-226 190 1490-1836 1524 1715 Dorsal thoraco-lumbar 142-177 163 1967-2413 2224 2387 Dorsal sacrum 108-142 124 1576—1990 1741 1865 Tail 100-176 135 1273-1500 1402 1537 Anus 86-137 114 1521-1837 1638 1752 Vulva Lateral abdomen 64-111 84 2222-2519 2392 2476 Lateral thorax 97-132 116 2264-2703 2440 2556 Lateral brachium 175-208 189 2146-2487 2334 2523 Axilla 72-136 88 1734-2127 1921 2010 Medial carpus 100-168 140 1648-1919 1719 1859 Lateral carpus 296-378 334 1680-2001 1771 2105 Ventral thorax 127-164 114 839—1349 1176 1320 Ventral abdomen 111-140 126 1100-2298 1830 1956 Prepuce 109-131 121 1173-1826 1584 1805 Interdigital area 170-203 186 1630-2100 1809 1996 Key: A = Average of six measurements determining epidermal and dermal thicknesses Total skin thickness Average epidermal thickness plus average dermal TS E+D thickness * = Measured in microns TABLE 2 MEASUREMENTS OF EPIDERMAL, DERMAL, AND TOTAL SKIN THICKNESSES (Male 2) AREA RENEEERMISA RANGEERMIS.A EED Lip 149-170 159 1140-1472 1308 1476 Snout 242-302 271 1889-2460 2173 2445 Bridge of nose 186-242 219 997-1346 1112 1332 Eyelid 62-107 70 Ear 90-144 114 632- 900 786 900 Dorsal neck 84-142 105 1837-2229 2057 2162 Dorsal thoraco—lumbar 155-196 178 2331-2636 2426 2605 Dorsal sacrum 119-160 143 2274-2601 2420 2563 Tail 116-136 125 1097-1562 1362 1488 Anus 127-151 144 1268-1689 1553 1698 Vulva Lateral abdomen 72-122 104 2292-2769 2538 2643 Lateral thorax 98-162 131 2336-2612 2575 2706 Lateral brachium 112-146 129 1970-2209 2053 2183 Axilla 60- 94 77 988-1377 1193 1271 Medial carpus 120—157 138 764-1300 1102 1241 Lateral carpus 150-193 170 1366-1794 1621 1792 Ventral thorax 81-133 108 1400-1848 1675 1784 Ventral abdomen 71-117 93 1597-1880 1753 1846 Prepuce 98-146 115 1401-1777 1629 1744 Interdigital area 160-203 182 1784—2333 1955 2137 Key: and dermal thicknesses TS E+D thickness Total skin thickness Average epidermal thickness plus average dermal * = Measured in microns A = Average of six measurements determining epidermal 22 TABLE 3 MEASUREMENTS OF EPIDERMAL, DERMAL, AND TOTAL SKIN THICKNESSES - (Male 3) S Lip 123-182 157 1320-1627 1514 1671 Snout 197-261 232 2090-2791 2353 2585 Bridge of nose 139-174 159 1207—1398 1349 1508 Eyelid 86-121 99 Ear 66-116 93 564- 834 636 730 Dorsal neck 135-162 149 1453-1802 1698 1848 Dorsal thoraco-lumbar 143-194 165 1989-2377 2116 2281 Dorsal sacrum 167-198 185 2061-2494 2249 2434 Tail 120-144 131 1200-1690 1399 1531 Anus 92-130 117 1888-2274 2009 2127 Vulva Lateral abdomen 122-142 126 2121-2359 2206 2332 Lateral thorax 109-121 115 2263-2777 2587 2703 Lateral brachium 130-177 152 1685-1944 1837 1989 Axilla 71-129 87 1308-1829 1617 1704 Medial carpus 99-170 134 827-1020 945 1079 Lateral carpus 136-171 155 1566-1841 1705 1860 Ventral thorax 177-209 191 1139-1394 1325 1517 Ventral abdomen 88-119 90 1447-1838 1649 1740 Prepuce 100-170 133 1500-2130 1797 1930 Interdigital area 199—294 223 2023-2490 2274 2497 Key: and dermal thicknesses TS E+D thickness Total skin thickness Average epidermal thickness plus average dermal * = Measured in microns A = Average of six measurements determining epidermal 23 TABLE 4 MEASUREMENTS OF EPIDERMAL, DERMAL, AND TOTAL SKIN THICKNESSES (Female 1) Lip 127-154 141 1502-1772 1652 1793 Snout 211-279 223 2033-2521 2249 2472 Bridge of nose 152-182 164 764-1246 1081 1264 Eyelid 91-125 106 Ear 148-182 163 629- 993 823 986 Dorsal neck 144-230 189 1640-1993 1839 2028 Dorsal thoraco-lumbar 160-212 183 1539-1878 1771 1954 Dorsal sacrum 140-188 166 1430-1801 1642 1808 Tail 154-219 188 1711-1911 1874 2062 Anus 113-156 128 1720-2120’ 1946 2074 Vulva 120-173 141 1372—1880 1632 1773 Lateral abdomen 161-222 169 1571-1957 1766 1936 Lateral thorax 119-158 145 1840-2380 2156 2301 Lateral brachium 134-201 174 1606-1855 1756 1930 Axilla 69-136 96 1321-1740 1592 1688 Medial carpus 194-251 224 1290—1711 1536 1761 Lateral carpus 149-191 170 1116-1582 1389 1559 Ventral thorax 118-174 146 1240-1700 1572 1718 Ventral abdomen 107-149 130 1289-1597 1409 1539 Prepuce Interdigital area 170-211 184 1827-2249 1940 2125 Key: A = Average of six measurements determining epidermal and dermal thicknesses TS E+D thickness Total skin thickness Average epidermal thickness plus average dermal * = Measured in microns 24 TABLE 5 MEASUREMENTS OF EPIDERMAL, DERMAL, AND TOTAL SKIN THICKNESSES (Female 2) AREA EPIDERMIS DERMIS TS RANGE* A RANGE A E+D Lip 176-228 205 1264-1597 1425 1631 Snout 769-968 928 2382-2808 2622 3550 Bridge of nose 271-342 308 1622-1914 1852 2160 Eyelid 82-137 105 Ear 93-136 125 714- 937 829 954 Dorsal neck 122-173 141 2062—2571 2285 2426 Dorsal thoraco-lumbar 99-136 151 1901-2248 2003 2154 Dorsal sacrum 87-160 145 1381—1785 1680 1826 Tail ' 139-200 155 2049-2384 2249 2404 Anus 106-154 139 1737-2267 2116 2255 Vulva 86-160 125 1900-2178 2033 2158 Lateral abdomen 80-126 116 3212-3770 3517 3636 Lateral thorax 78-119 107 1986-2575 2227 2334 Lateral brachium 83-146 114 1655-2029 1875 1990 Axilla 61-101 85 1500-1944 1722 1808 Medial carpus 165-227 190 1276-1833 1580 1770 Lateral carpus 99-163 124 1071-1361 1220 1344 Ventral thorax 102-157 129 2040-2387 2190 2319 Ventral abdomen 82-130 107 1169-1551 1480 1588 Prepuce Interdigital area 206—334 271 1220—1746 1414 1668 Key: and dermal thicknesses TS E+B thickness Total skin thickness Average epidermal thickness plus average dermal * = Measured in microns A = Average of six measurements determining epidermal 25 TABLE 6 MEASUREMENTS OF EPIDERMAL, DERMAL, AND TOTAL SKIN THICKNESSES (Female 3) AREA EPIDERMIS DERMIS TS RANGE* A RANGE A E+D Lip 90-179 142 1737-1920 1816 1958 Snout 689-1337 941 3223-4377 3802 4754 Bridge of nose 210-357 272 1999-2564 2499 2771 Eyelid 78-120 106 Ear 152-194 171 876-1160 1076 1247 Dorsal neck 157-224 186 3072-3684 3475 3661 Dorsal thoraco-lumbar 148-198 170 2988-3502 3292 3462 Dorsal sacrum 130-198 176 2603-3245 2998 3175 Tail 140-237 182 1860-2551 2116 2299 Anus 112-162 130 2300-2766 2482 2612 Vulva 90-134 117 2041-2228 2146 2263 Lateral abdomen 110-157 125 1978-2443 2271 2396 Lateral thorax 86-143 119 2004-2676 2316 2436 Lateral brachium 97-152 131 1755-2294 2000 2131 Axilla 89-123 103 1639-2277 2112 2215 Medial carpus 111-159 131 1140-1500 1357 1489 Lateral carpus 99-129 115 1226-1518 1416 1531 Ventral thorax 109—163 140 1411-1716 1524 1664 Ventral abdomen 92-133 110 1632-2122 1897 2007 Prepuce Interdigital area 294-472 374 1470-1888 1720 2095 Key: and dermal thicknesses TS E+D thickness Total skin thickness Average epidermal thickness plus average dermal * = Measured in microns A = Average of six measurements determining epidermal RESULTS AND DISCUSSION Skin Thickness Statistical significance of the skin measurements was determined by the Sign test and by using the Kelley Sta- tistical Tables. The epidermis of female hogs was significantly thicker than castrated males ( .01 levell Montagna (1956) reported that testosterone increases the rate of mitotic activity in the epidermis and consequently the thickness of the epider- mis. He further stated testosterone increases the thick- ness of the skin over the entire body of man. Thyroxine and testosterone are thought to be antagonistic in main- taining the epidermis of rats. Thyroxine produces a thin epidermis with decreased mitotic activity, whereas testos- terone has the opposite effect (Earthy and Grad, 1951). Since the males in this study were castrated, their epi- dermis would be expected to be thinner than the females. Estrogens are said to have a mitogenic effect on the epi- dermis in the adult female mouse (Bullough, 1950). The female dermis was significantly thicker than the castrated males ( .05 level). Castor (1950) reported hog ‘ACTEIextract applied locally to the skin of adult normal 26 27 rats resulted in a thinner dermis in both sexes, colla- genous fibers were fused giving the dermis a homogeneous appearance, elastic fibers were not effected, and the numbersof cells in the dermis were reduced. Endocrinol— ogists generally agree that castrated animals will produce greater quantities of ACTH than normal animals. The hypothesis that the total skin thickness of female hogs was thicker than male hogs was rejected at the .05 level. The thickest epidermal areas were generally found on the snout and interdigital area, and the thinnest in the axilla, eyelid and ventral abdomen. The epidermis on the snout of two of the females measured over 900 microns, due to a very thick stratum corneum. The thickest dermal areas were usually present on the snout and lateral abdomen, and thinnest on the ear and medial carpus. Generally the dorsal skin was thicker than the ventral in both sexes. Epidermis The epidermis conSisted of a continuous layer of strati- fied squamous epithelium, in which were found such epidermal 28 appendages as hair, sebaceous glands and sweat ducts. It included only three characteristic layers since the stratum lucidum was absent (Plate II). This was in agreement with Moritz and Henriques (1947), Smith (1960), and Fowler (1962) who did not observe a stratum lucidum in their investiga- tions of swine integument. Stratum corneum. The stratum corneum was present in all sections studied, however its thickness varied greatly in different body areas. It was thickest in the snout, which is to be expected since swine utilize their snout as a discriminatory organ. The interdigital skin, which pos— sessed a thick stratum corneum, was characterized by sharp epidermal projections (Plate XVIII). This cornified layer was thin in the eyelid, axilla, and dorsal areas of the abdomen and thorax. Individual cells were not apparent in most sections, and distinct cell outlines were rarely ob- served (Plate II). In the keratinized cells where the cell outlines remained distinct, nuclear fragments were apparent. The keratin was not always densely packed and often arti- facts in the form of large spaces were seen between the layers of keratin (Plate XVIII, XV). Stratum granulosum. The stratum granulosum generally consisted of 1 to 5 layers of flat, polygonal cells filled 29 with basophilic granules (PlateII, XV, XIII). This layer was thickest in areas of thick skin (snout and inter- digital skin), and only one layer in thickness or occasion- ally sporadic in thin skin (eye, axilla). Many of the cells possessed fragmented nuclei. Contrary to this work, Ellen- berger (1906) reported the absence of this layer on the snout of hogs. Stratum germinativum. The cells of the stratum germi- nativum varied from squamous or polygonal, in the more super- ficial parts, to columnar or cuboidal, at the basal portion. The cells of the stratum spinosum, which were larger than the basal cells, possessed definite intercellular bridges prominent in the snout and interdigital skin (Plate II). "Clear cells,‘ which were observed primarily in the stratum germinativum, possessed a clear cytoplasm and baso- philic nucleus (Plate XXII). Mitosis was limited to the basal layer and deeper lay- ers of the stratum spinosum (Plate XVI). According to Flatten (1896) mitotic division in the deepest three layers of epidermis in the snout of the pig was noted by Flemming in 1844. 3O Dermis The dermis was subdivided into two layers, which blended without a distinct demarcation (Plate XV, XXI). The papillary layer originated immediately beneath the epi— dermis and the deeper portion of the dermis was the reticu— lar layer. Contrary to Wilson (1941), a definite reticular layer was observed. Beneath the reticular layer a promi— nent layer of adipose tissue (panniculus adiposus) was noted, which was sharply delimited from the more super- ficial layer (Plate XVII). Strands of connective tissue from the reticular layer extended throughout the panniculus adiposus, generally perpendicular to the surface of the skin. NUmerous eosinophils were noted throughout the entire dermis, the greatest concentrations being noted in the papillary layer of the females. Numerous capillary plexuses were present in the papil- lary layer and in the surrounding connective tissue sheaths of hair follicles and sebaceous glands (Plate XIII, XVII, XXII. According to Fowler (1962) the first elastic tissue fibers were observed throughout the reticular layer in the ventral body areas and limbs of 95-day-old fetuses. Smith 31 (1960) did not observe elastic fibers in the dermis of newborn swine. Elastic fibers coursed throughout the entire dermis, forming complex networks (Plate XV). Individual fibers ranged in thickness from 1 to 5 microns. They extended between the collagenous bundles without a definite arrange— ment. Smith (1960) did not observe elastic fibers in the dermis of newborn swine. Delicate elastic fibers were noted in the trabecula of tactile hairs (Plate V), and in the surrounding collagenous sheath of both ordinary and tactile hair follicles (Plate V, XVI). Elastic fibers of the dermis extended into the elastic cartilage of the ear, anchoring the cartilage to the connective tissue (Plate XX). These fibers were also noted in the bulbs of hair folli- cles (Plate XVI). The heaviest concentration of elastic fibers was located in the preputial skin and snout. In agreement with Wilson (1941), the papillary layer possessed a heavier concentration of these fibers than the reticular layer. The dorsal body areas were more densely infiltrated with elastic fibers than the ventral areas. Mast cells were scattered throughout the entire dermis in varying numbers. There was a greabudensity of mast cells 32 in the papillary layer than in the reticular layer. This might be due to the greater concentration of collagenous bundles in the latter, which prevented their observation. In a qualitative examination, the mast cells appeared more numerous in female than male dermis. The greatest concen- tration of mast cells in the female dermis was observed in the anal region and axilla. Mast cells were heaviest around blood vessels of both sexes (Plate XIX). _Smith (1960) did not observe mast cells in newborn swine. Holmes (1960) reported two types of mast cells in rat integument, small, polymorphous ones in the papillary layer and larger ones in the reticular layer and hypodermis, but only one type was observed in this study. The papillary layer was composed of loosely arranged connective tissue elements. The collagenous bundles of the papillary layer were delicate and thin in contrast to those of the reticular layer (Plate XV). However, in the anal wmqud regionfland ear the collagenous bundles of both layers were similar in thickness (Plate XXI). Usually the collagenous bundles paralleled the surface of the skin, however, they followed a perpendicular course as they extended into the dermal papillae (Plate XV). 33 The reticular layer was thicker than the papillary layer and generally had thicker collagenous bundles.) These thick bundles, some of which measured up to 100 microns, usually extended parallel to the surface of the skin. Collagenous bundles were generally thicker and more densely arranged in the female hogs and thickest on the ventral and medial body areas of both sexes. Isolated groups of fat cells were observed in the deeper portions of the reticu- lar layer. Hair The general structure of hair was in agreement with the findings of Montagna and Ellis (1952) and Trautmann and Fiebiger (1957). As Flatten (1896), Ellenberger (1906), and Smith (1960) reported, the hair was usually arranged in groups of three, however single hairs and groups of two and four were frequently seen (Plate VI, VII, VIII). Smith (1960) observed single hairs and groups of four and six. Fowler (1962) reported groups of 3 to 5 hairs. The central hair of a triad was generally larger than the two adjacent hairs, however several triads were observed in which the hairs were all the same relative size (Plate VIII). Smith 34 (1960) reported only one hair was found per follicle regard- less of the size of the hair. This observation conflicts with those of Fowler (1962) and the author. Several folli- cles were noted in which two hairs projected toward the sur- face of the skin, one hair being larger and occupying the greater volume of the follicle (Plate VI, VIII Arrector pili muscles were attached to the connective tissue sheath about half way down the follicle. A local- ized thickening of the epithelial root sheath marked the. point of attachment (Plate XVII). Occasionally a single arrectores pilorum muscle extended to two of the follicles in a group and two arrector pili muscles were observed to attach to a single follicle (Plate IX, X). "Follicular folds," evident in many of the hair folli- cles studied, formed one to twenty three corrugations in the outer epithelial root sheath (Plate XI, XII, XXII). "Follicular folds" were located immediately superior or inferior to the sebaceous gland openings. Folds were not observed at both sites in the same follicle as was demon- strated by Smith (1960). Fowler (1962) observed folds inferior to the sebaceous gland opening. These corruga- tions generally exhibited a smooth, continuous membrane- 1ike surface at the lumenal end (Plate XI). The cells 35 within the corrugations were smaller than those of the stratum cylindricum and irregularly placed. The shapes of the follicular corrugation cells varied from oval to a very flat, elongated type. Pyknotic nuclei were frequently observed in these cells. Various functions have been attributed to these folli- cular infoldings. Strickland (1958) stated that these folds may be related in some way to the movement of sebum to the surface of the skin. Holmes (1960) attributed their presence to the relaxed position of the hair follicles. Smith (1960) stated that both these factors may be involved in making possible an "emergency" supply of sebum to the skin. These infoldings may have been true follicular struc- tures or artifacts. Montagna and Ellis (1952) reported the absence of these corrugations in the human species, indica— ting they may be specialized structures limited to domestic animals. 0n the other hand, the corrugations superior to the sebaceous gland opening would be an impediment to the transport of sebum toward the surface of the skin, indica- ting possibility of artifact. The artifact theory may be further supported by the hypothesis that when the animal 36 was sacrificed, the supporting elements of the follicle lose their dynamic state and contract, resulting in folds. Tactile hairs. Prominent tactile hairs were seen in the lip and snout. Smith (1960) reported tactile hairs only in the snout. Fowler (1962) observed tactile hairs on the snout, jowl and eyelids. The tactile hairs were arranged singularly in both the lip and snout, and were surrounded by a thick connective tissue sheath (Plate III). Trabeculae, composed of collagenous and elastic fibers, traversed the blood sinus of the hairs (Plate III, IV). A single large nerve appeared to innervate this structure (Plate IV). Arrector pili muscles were not Observed in relation to the tactile hairs, supporting previous reports (Smith, 1960; Fowler, 1962) that the tactile hairs are not supplied by these muscles. Sebaceous Glands During the development of the hair follicle, epithelial cells from the side of the follicle, which made an obtuse angle with the skin, grew into the dermis to form sebaceous glands. The sebaceous glands observed were simple alveolar or simple branched alveolar glands which opened, by very 37 short ducts, into the neck of the hair follicles (Plate XXII). These glands were composed of a secretory portion and an excretory duct. The cells of the secretory portion of the gland varied in size and structure. The basal cells were small in relation to those of the central part (Plate XI, XXII). The basal cells, which were small cuboidal, possessed definite nuclei and nucleoli. The central cells, 3 to 4 times larger than the basal cells, showed bizarre shapes and pyknotic nuclei, while the nucleus was entirely missing in some of the cells (Plate XI, XXII). The cyto- plasm of these cells appeared vacuolated, indicating degen- eration (Plate XI). Generally, one duct opened into the hair follicles, however in some cases two ducts were ob- served, one on either side of the follicle. Cellular frag- ments were noted in some of the excretory ducts, indica- ting glandular activity. In cross section, the sebaceous glands were arranged in a rosette fashion around the folli- cles (Plate XXI). Sweat Glands In agreement with Trautmann and Fiebiger (1957), the sweat glands observed were simple coiled tubular apocrine 38 glands. The latter were found in all areas with the excep- tion of the snout, where tubular merocrine glands were ob— served. Smith (1960) and Fowler (1962) reported compound tubular sweat glands in the snout of newborn and fetal swine. Flatten (1896) reported numerous sweat glands in the snout of pigs. The secretory portion of the glands was located in the lower areas of the reticular layer and throughout the pan- niculus adiposus (Plate VII, XVII, XVIII), the largest glands being in the axilla and anal region and the smallest in the eyelid and external ear (Plate XXI). Various phases of activity were observed in these glands. In many of the glands, the apical portions of the secretory cells protruded into the lumen (Plate XXIV). In other glands, the fragmented apical portion was seen in the lumen with what appeared to be secretion from these cells (Plate XXIII). Resting phases of the cells were also noted (Plate XXIII). These several anatomical‘observations strongly suggest that the sweat glands of Yorkshire hogs may be functional. Carpal glands. Carpal glands were not evident in any of the sections studied. Gross observation of the medial carpus of ninety additional Yorkshire hogs also proved fruitless. SUMMARY AND CONCLUSIONS The skin of three mature female and three mature cas— trated male YOrkshire hogs was studied histologically. The epidermis included only three characteristic layers since the stratum lucidum was absent. The stratum corneum was thickest in the snout and interdigital skin and the latter was characterized by sharp epidermal projections. The thinnest stratum corneum was found in the eyelid, axilla, and dorsal areas of the abdomen and thorax. The stratum granulosum was thickest in areas of thick skin (snout, interdigital skin) and only one layer in thickness or occasionally sporadic, in thin skin (eye, axilla). "Clear cells," were observed only in the stratum germina- tivum. Mitosis was limited to the basal layer and deeper layers of the stratum spinosum. The thickest epidermis was found on the snout and interdigital skin and the thinnest on the axilla, eyelid and ear. In the dermis, prominent layers of adipose tissue (pan- niculus adiposus) were noted beneath the reticular layer. Elastic fibers, which coursed throughout the entire dermis, were observed in the trabecula of tactile hairs and in the bulbs of hair follicles. The heaviest concentration of 39 40 these fibers was found in the snout and prepuce. The papillary layer possessed a heavier concentration than the reticular layer and the dorsal body areas were more densely infiltrated than the ventral areas. There was a greater concentration of mast cells in the papillary layer than in the reticular layer. Qualitatively, the mast cells appeared more numerous in female than male dermis, the greatest concentration in the female dermis was observed in the anal region and axilla. The collagenous bundles of the papillary layer were delicate and thin in contrast to those of the reticular layer. However, in the anal region and ear the collagenous bundles of both layers were similar in thickness. Usually, the collagenous bundles paralleled the surface of the skin, however they followed a perpendicular course as they extend- ed into the dermal papillae. The collagenous bundles were generally thicker and more densely arranged in the female hogs and thickest on the ventral and medial body areas of both sexes. The hair was usually arranged in groups of three, how- ever individual hairs and groups of two were frequently seen. The central hair of a triad was generally larger than the 41 two adjacent hairs, however several triads were observed in which the hairs were all the same relative size. Several follicles were noted which possessed two hairs, one hair being larger and occupying the greater volume of the folli- cle. "Follicular folds" formed one to twenty three corruga- tions in the outer epithelial root sheath. These folds were located either superior or inferior to the sebaceous gland openings. Prominent tactile hairs were arranged singly in both the lip and snout. A The sebaceous glands, which were simple alveolar or simple branched alveolar glands, appeared to be active. The central cells, 3 to 4 times larger than the basal cells, showed bizarre shapes and pyknotic nuclei, however the nu- cleus was entirely missing in some of the cells, indicating degeneration of the cells. The sebaceous glands were ar- ranged in a rosette fashion around the follicles. Simple, coiled, tubular apocrine sweat glands were observed in all body areas with the exception of the snout, where tubular merocrine glands were present. The largest sweat glands were noted in the axilla and anal region, and the smallest in the eyelid and external ear. The sweat glands appeared to be active in all areas examined. 42 Carpal glands were not evident in any of the sections studied. Gross observation of 90 additional Yorkshite hogs failed to indicate any sign of these glands. LITERATURE C I TED Adolph, W. E., R. F. Baker and G. M. Leily. 1951. Electron microscope studies of epidermal fibers. Science 113:685-686. Andrew, W. and N. V. Andrew. 1949. Lymphocytes in the normal epidermis of rat and man. Anat. Rec. 104:217— 241. Baumann, E. S., C. F. Gessert and B. H. Senturia. 1958. Studies of factors considered responsible for diseases of the external ear. School of Aviation Medicine, U.S.A.F. Randolph A.F.B. Texas. Baumberger, J. P., v. Suntzeff and E. v. Cowdry. 1942.' Methods for the separation of epidermis from dermis and some physiologic and chemical properties of isolated epidermis. Jour. Nat. Cancer Inst. 12:413- 423. Billingham, R. E. and P. B. Medawar. 1947. The cyto- genetics of black and white guinea pig skin. Nature 159:115-117. Cooper, Z. K. and H. C. Franklin. 1940. Mitotic rhythm in the epidermis of the mouse. Anat. Rec. 78:1-8. Copenhaver, W. M. and D. D. Johnson. 1958. Bailey's Textbook of Histology. Williams and Wilkins Co. Cowdry, E. V. and H. C. Thompson. 1944. Localization of maximum cell division in the epidermis. Anat. Rec. 88:403-409. Craft, W. A. 1932. The inheritance of hair whorles (in swine). Proc. Okla. Acad. Sci. 12:7-8. Crossmon, G. 1937. A modification of Mallory's connective tissue stain with a discussion of the principles involved. Anat. Rec. 69:33-38. 43 44 Dawson, H. L. 1948. Lambert's Histology. The Blakiston Company, Philadelphia. David, E. T. 1932. Histology of the skin of the Mexican hairless swine (Sus scrofa). Amer. Jour. Anat. 50:283- 292. Dick, J. S. 1947. Observations on the elastic tissue of the skin with a note on the reticular layer at the junc- tion of the dermis and epidermis. Jour. Anat. 81:201- 211. Dixon, A. D. 1961. The innervation of hair follicles in the mammalian lip. Anat. Rec. 140:147-158. Ellenberger, W. 1906. Handbuch der vergleichenden mikro- skopischen Anatomie der Haustiere. Verlagsbuchhandlung Paul Parey, Berlin. pp. 125-190. Findlay, J. D. and D. M. Jenkinson. 1960. The morphology of bovine sweat glands and the effect of heat on the sweat glands of the Ayrshire calf. J. Agri. Sci. 55: 247-249. Flatten, W. 1896. Untersuchungen fiber die Haut des Schwein. Inaug. Diss. Berlin. Fowler, E. H. 1962. The Developmental Histology of the Integument of Fetal Pigs. Thesis. Michigan State University. Goldsberry, S. and M. L. Calhoun. 1955. The comparative histology of the skin of Hereford and Aberdeen Angus cattle. Am. Jour. Vet. Res. 20:61-68. Gray, M., H. Blank and G. Rake. 1952. Electron microscopy of normal human skin. Jour. Invest. Dermatol. 19:449- 457. Guyer, M. F. 1949. Animal Micrology. University of Chicago Press, Chicago. 45 Ham, A. W. and C. O. Leeson. 1961. Histology. J. B. 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Effects of ACTH applied locally to the skin of normal rats. Jour. Endocrin. Earthly , H. and B. Grad. I95]. Influence of testis and thyroid hormones on the epidermis of the male albino rat. Anat. Rec. Hfik28 48 Plate II Compact, thick, cellular, stratum corneum with nuclear remnants-—vertical section of the snout. H. and E. stain. 280x. 1. Stratum corneum 2. Stratum granulosum 3. Stratum germinativum 50 Plate III The individual arrangement of tactile hairs-- horizontal section of the lip. H. and E. stain. 62X x ‘ ~ in]. ‘M.’ y f c . I . .4 . . a., .71 174.01: q‘fi 52 Plate IV A single tactile hair. NOte the large nerve and smaller nerve branches in the capsule—- horizontal section of the lip. H. and E. stain. 102x Connective tissue capsule Blood sinus Trabeculae Hair Nerves Blood vessels Adipose tissue 54 Plate V Elastic fibers in the trabecula of a tactile hair--horizontal section of the lip. Weigert's and Van Gieson's stain. 1083X 1. Blood sinus 2. Trabecula 3. Connective tissue capsule 4. Elastic fibers ‘1. 56 Plate VI The hair pattern showing characteristic triads. Note the two hairs in a single follicle--hori- zontal section of the bridge of the nose. H. and E. stain. 51X 1. Follicles with two hairs 2. Epidermis 1... #2 a. lo I O) ‘7 - .I i Ill . O . i , F v I. .1. . . . . .‘li ., I . a I . I / -./l a. .u/ . u o .I . n . I ,1). . . . a -. I . . .1 r .. . . l ' d l . . I O r 4 . . v. .. o I, . _ .4 . . I I a .. a , . ,.. . . r t . l v . 41,! I . . . . my a . c . 4 u. ;v . I I. v . . 0 I | A l . I. I 58 Plate VII The hair pattern showing triads and groups of two--horizontal section of the medial carpus. H. and E. stain. 57X 1. Two hairs in a single follicle 2. Sweat glands 3. Adipose tissue 4. Capillaries 60 Plate VIII A triad, the hairs are the same relative size--horizonta1 section of the lateral brachium. H. and E. stain. 165x 1. Adipose tissue 2. Sweat glands 62 Plate IX A single arrector pili muscle attached to two hair follicles--horizonta1 section of the dor- sal sacrum. H. and E. stain. 170X 1. Arrector pili muscle 64 Plate X A single hair follicle with two arrector pili muscles--horizontal section of the dorsal thoraco-lumbar region. H. and E. stain. 140x 1. Duct of sweat gland 2. Arrector pili muscles 66 Plate XI Follicular folds and surrounding sebaceous glands. Note the cellular degeneration in the sebaceous glands--vertica1 section of the bridge of the nose. H. and E. stain. 360X 1. Lumen of the follicle 2. Cuticle of the follicle 3. Follicular folds 4. Degenerating cells of the sebaceous gland 68 Plate XII Follicular folds--vertical section of the bridge of the nose. H. and E. stain. 375x 1. Lumen of the follicle 2. Follicular folds 3. Cuticle of the follicle 70 Plate XIII Follicular fold-like structures at the bulb of the hair follicle--vertical section of the upper eyelid. H. and E. stain. 164X Cortical pre-keritinization area Follicular fold—like structures Cuticle of the follicle Lumen of the follicle Capillaries Skeletal muscle Clear cells . \. ...\2\. , 4 ~ Hun. “a“ . v ,. , xx . 5. .4. m A i ' a y. .n \A 72 Plate XIV Two hairs in a single follicle--vertical section of the upper eyelid. H. 1. and E. stain. 140X Epidermis Ducts of sweat glands Skeletal muscle Keratin Main hair Smaller hair .. ..u .....,.......,.o... I 2. 34):”.le . m¢fi -- f. p t\ \ \.’/3 .u’ .’ ’ 74 Plate XV Arrangement of the dermal fibers showing the papillary and reticular layer. Note the elastic fibers-—vertical section of the lateral thorax. Weigert's and Van Gieson's stain. 164x 1. Stratum corneum 2. Stratum granulosum 3. Stratum germinativum 4. Papillary layer 5. Reticular layer 6. Elastic fibers 7. Collagenous fibers 76 Plate XVI Elastic fibers in the dermal papilla of a hair follicle--vertical section of the bridge of the nose. Weigert's and Van Gieson's stain. 452x 1. Connective tissue sheath Outer epithelial root sheath Inner epithelial root sheath Proliferating cortex of the hair Dermal papilla Various stages of mitosis 78 Plate XVII An arrector pili muscle attached to the bulge of the outer epithelial root sheath--horizontal sec- tion of the prepuce. H. and E. stain. 74X Reticular layer Panniculus adiposus Sebaceous gland Sweat glands Arrector pili muscle Capillary plexus , . ."o 1 .“ W". ' I ' I 1 . g ' 1 q ‘ .I ‘ i. .I ‘ .'5 v, .I N w. ' 0 ' I i‘ .' v- F ' E ll 0 ' I i" . . .' l.‘.t‘l ‘ ' I . 80 Plate XVIII Epidermal projections of the interdigital skin-—vertical section. H. and E. stain. 110x 1. Keratin 2. Epidermis 3. Sweat glands 82 Plate XIX Mast cells and eosinophils in the reticular layer of the dermis--horizonta1 section of the ventral abdomen. Giemsa's stain. 540x 1. Mast cell 2. Eosinophil 3. Blood vessel 84 Plate XX Elastic fibers of the cartilage projected into the adjacent dermis. NOte the absence of a panniculus adiposus--vertica1 section of the external ear. Weigert's and Van Gieson's stain. 352x 1. Elastic cartilage 2. Elastic fibers 3. Capillary 4. Dermis 86 Plate XXI The arrangement of sebaceous glands around hair follicles. Note that there is little difference in the size of the collagenous bundles in the papillary and reticular layer, also the absence of a panniculus adiposus--vertical section of the upper eyelid. H. and E. stain. 64X 1. Hair follicles 2. Sebaceous glands 3. Skeletal muscle 4. Sweat glands 5. Sweat gland ducts 6. Papillary layer 7. Reticular layer 8. Blood vessels 88 Plate XXII Ducts of the sebaceous gland opening into the hair follicle. Note the numerous capillaries in the surrounding connective tissue sheath-— vertical section of the upper eyelid. H. and E. stain. 200x 1. Degenerating cells of the sebaceous gland 2. Debris of the sebaceous glands 3. Follicular fold 4. Duct of sebaceous gland 5. Capillaries :. .'_ i‘ 4 " i 1 i h“ (M). Wt“ i“ . . ~ c‘ ”i r A r :5. 34¢ 5'.- . it i H h": . H e "" 90 Plate XXIII Resting phase of the apocrine sweat glands. Note the debris in the gland 1umen--horizontal section of the dorsal sacrum. H. and E. stain. 424x 1. Myoepithelium 2. Secreted debris in the lumen 3. Adipose tissue 92 Plate XXIV Apocrine sweat gland in the secretory phase. Note the prominent myoepithelium--vertical section of the dorsal sacrum. H. and E. stain. 912x 1. Myoepithelium 2. Adipose tissue