10 



Anatomy of the; Rabbit. 



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ducts of the urinogenital organs. In all epithelia the cellular feature is a 

 prominent one, and it is largely for this reason that as lining membranes 

 they are not conspicuous in gross structure. They are noteworthy, 

 however, for their products, the hairs and the various kinds of secreting 

 organs or glands. 



The epithelium of the skin (Fig. 2, ep.) is known as the epidermis or 

 scarf-skin. Although composed of several layers of cells, it forms 

 an exceedingly thin membrane, extending over the surface of the body 

 and connecting at certain points with the epithelia of the internal 

 surfaces. It is supported by a layer of connective tissue which forms the 

 true skin or cerium. 



The epithelium of the internal surfaces forms the chief portion 

 of the mucous membranes, and in the greater portioa of the alimen- 

 tary tract the epithelial layer is asso- 

 ciated with a thin layer of smooth 

 ,^~ssg=^-:i: .^ , _.,^ muscle to form a mucous tunic 



(Fig. 15, t.ms.). 



The coating of hairs on the surface 

 of the body, the presence of which is 

 a notable mammalian feature, is a 

 protective investment arising from 

 the epidermis. A hair is produced by 

 the modification of the central por- 

 tion of an ingrowth of the epidermis, 

 termed the hair follicle (Fig. 2, f.). 

 The latter contains at its base a 

 small elevation of the underlying 

 vascular connective tissue, the hair 

 papilla, through which the structure 

 is nourished. On the general surface 

 of the body the hair follicles are 

 arranged in groups (Fig. 4), and on 

 the lips certain large follicles are set 

 apart for the production of the 

 greatly enlarged sensory hairs or 

 vibrissae. Connected with the hair 

 follicles are thin strands of smooth 

 muscle, the arrectores pilorum (Fig. 2, 

 a. p.). They are placed in the broad 

 angles formed by the inclined follicles 

 with the corium, and their contrac- 

 tion throws the hair into a more 

 nearly erect position. 

 Epithelial glands are ingrowths of the general layer, the cells of which 

 become greatly modified as secreting structures. The lumen or cavity 

 of the gland, in most cases greatly complicated through the division of 

 the gland substance, is connected with the general surface by a duct 

 which thus serves to carry away its secretion. In some cases the con- 

 nection of a gland with the epithelial surface is embryonic, and in the 



Fig. 2. From a section of the tipper lip of a 

 four-day-old rabbit: a. p., erector muscle of 

 the hair (a.pi', is that of the adjacent fol- 

 licle); c.t., connective tissue of the corium; 

 ep., epithelium; f., hair follicle; s., hair 

 shaft; s.g., sebaceous gland. 



