432 DISEASES OF THE HORSE. 



STRUCTUEE OF THE SKIN. 



The skin consists primarily of two parts : (1) The superficial non- 

 vascular (without blood vessels) layer, the cuticle, or epidermis; and 

 (2) the deep vascular (with blood vessels) layer, the corium, dermis, 

 or true skin. 



The cuticle is made up of cells placed side by side and more or less 

 modified in shape by their mutual compression and by surface evapo- 

 ration and drying. The superficial stratum consists of the cells dried 

 in the form of scales, which fall off contiimally and form dandruff. 

 The deep stratum (the mucous layer) is formed of somewhat rounded 

 cells with large central nuclei, and in colored skin containing numer- 

 ous pigment granules. These cells have prolongations, or branches, 

 by which they communicate with one another and with the superficial 

 layer of cells in the true skin beneath. Through these prolongations 

 they receive nutrient liquids for their growth and increase, and pass 

 on liquids absorbed by the skin into the vessels of the true skin 

 beneath. The living matter in the cells exercises an equally selective 

 power on what they shall take up for their own nourishment and on 

 what they shall admit into the circulation from without. Thus, cer- 

 tain agents, like iodine and belladonna, are readily admitted, whereas 

 others, like arsenic, are excluded by the sound, unbroken epidermis. 

 Between the deep and superficial laj'^ers of the epidermis there is a, 

 thin translucent layer (septum lucidum) consisting of a double 

 stratum of cells, and forming a medium of transition from the deep 

 spheroidal to the superficial scaly cuticle. 



The time shin, or dermis, has a framework of interlacing bundles of 

 white and yellow fibers, large and coarse in the deeper layers, and 

 fine in the superficial, where they approach the cuticle. Between the 

 fibrous bundles are left interspaces which, like the bundles, become 

 finer as they approach the surface, and inclose cells, vessels, nerves, 

 glands, gland ducts, hairs, and in the deeper layers fat. 



The superficial layer of the dermis is formed into a series of minute 

 conical elevations', or papilla, projecting into the. deep portion of the 

 cuticle, from which they are separated by a very fine transparent 

 membrane. This papillary layer is very richly supplied with capil- 

 lary blood vessels and nerves, and is at once the seat of acute sensa- 

 tion and the point from which the nutrient liquid is supplied to the 

 cells of the cuticle above. It is also at this point that the active 



changes of inflammation are especially concentrated; it is the im- 



• ^ 



Description of Fig. 1, Plate XXXV : e. Epidermis, d. Derma. 1. Horny layer 

 of the epidermis. 2. Stratum mucosum. 3. Papillary layer of the derma. 4. 

 Excretory duct of a sudoriparous gland. 5. Glomerule of a sudoriparous gland. 

 6. Hair follicle. 7. Sebaceous gland. 8. Internal sheath of the hair follicle. 

 9. Bulb of the hair. 10. Mass of adipose tissue. 



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