642 TEGUMENTARY ORGANS. 



the skin the sebaceous glands abound without piliferous fol- 

 licles, but the piliferous follicles, when present, are always 

 accompanied with one or more, generally with two, sebaceous 

 glands. The numerous small follicles composing each of 

 these conglomerate sebaceous glands, communicate 'generally 

 with a single duct, sometimes with several ducts, which open 

 directly into the piliferous follicles, where they are present, 

 or on the surface of the skin in many hairless parts ; and 

 these glands vary in magnitude generally according to the 

 size of the hairs they accompany, but they are very minute 

 in the hog (146. C. e.) which has large hairs (146. C. d.). 



The piliferous follicles (146. A. C././.) are appropriated to 

 the development of the hairs, and to the reception of the 

 oily secretion of the sebaceous glands. They are elongated 

 simple sacs, widest at their deeper closed extremity, and nar- 

 rowest at their orifice, where they embrace closely the con- 

 tained hair. They penetrate vertically through the skin to 

 the subcutaneous cellular substance, and they correspond in 

 size and form with the contained hair. They are prolonga- 

 tions of the vascular secreting surface of the cutis, and they 

 receive the secretions of the sebaceous glands, which can be 

 pressed out from their orifice. Like all the ducts of cuta- 

 neous glands, they have a distinct lining of epithelium, which 

 can be drawn out entire, continuous with the epidermis, from 

 the macerated skin of the foetus, and coloured portions of 

 the cuticle can often be distinctly traced into their cavity. 

 The epidermic linings of these various small cutaneous 

 ducts, appear as so many minute connecting fibres, when the 

 cuticle is being gradually drawn off from the surface of the 

 cutis. 



The most exterior continuous tegumentary layer of animals, 

 as of other organized bodies, is the insensible extra vascular 

 epidermis, poured out as granular nuclei in a fluid medium, from 

 the reticulate, vascular, sensitive surface of the cutis, or secreted 

 by its capillaries. Like most internal organized tissues, the 

 exterior epidermic covering originates from minute cells, or cy- 

 toblasts, which possess, like entozoa, an independent means of 

 growth, and undergo various changes in the course of their de- 

 velopment ; and all the different cuticular appendages, as hairs, 

 spines, nails, hoofs, horns, feathers, and scales, are merely 

 aggregations of the same epidermic cells. The epidermic 

 nuclei when first formed, exhibit internally a granular struc- 



