TEGUMKXTARY ORGANS. 639 



CHAPTER EIGHTH. 



TEGUMENTARY ORGANS. 



THE animal body being an aggregate of numerous compli- 

 cated and delicate apparatus, nicely adjusted to the various 

 mechanical and chemical functions necessary for the sup- 

 port of life, is always protected externally from the action 

 of the surrounding elements and from accidental injuries, 

 by some common investing tegumentary organs. These ex- 

 ternal investments consist generally of a compact reticulate 

 fibrous, elastic, highly sensitive and vascular cutis, corium, 

 or true skin, and a more superficial, extravascular, insensible, 

 scaly cuticula, epidermis, or scarf-skin ; and to these are- often 

 superadded various forms of horny scales, plates, spines, hairs, 

 feathers, or other accumulated epidermic exudations from the 

 vascular secreting surface of the true skin. The cutis or true 

 skin of the higher classes of animals, developed, like the 

 osseous, the muscular, and the nervous systems, from the 

 exterior or serous layer of the germinal membrane of the 

 ovum, continues in the adult as the most exterior of the 

 sensitive and vascular tissues of the body. It is not only 

 the seat of the sense of touch, by the innumerable sensitive 

 vascular and erectile papillae developed over its surface, but 

 likewise of various secretions from myriads of minute glands 

 imbedded in its substance, and whose ducts traverse in a 

 straight or tortuous direction its fibrous tissue. These ducts 

 open on the surface of the epidermis, as seen in the annexed 

 views (Fig. 146.) from Gurlt, of the simple piliferous follicles 

 (146. A. C.f.f.) and the more complex sebaceous glands (146 

 A. h. C. e.) and sudoriferous glands (146. A. d. C. b. b.), com- 

 municating with the exterior surface of the skin (146. A. B. 

 C. a. a. .). Besides the piliferous follicles, the sudoriferous 

 and oil-glands, and the numerous capillary blood-vessels, 

 nerves, and lymphatics which every where permeate the 

 fibrous texture of the skin, it has been considered as the seat 



