HAIRS. CUTANEOUS GLANDS. 483 



upon a vascular papilla at the bottom of an epidermal pit (hair- 

 follicle) which projects into the dermis some distance below the 

 level of the epidermis (Fig. 257) ; the upper part or shaft pro- 

 jects freely on the surface of the skin. Each hair is composed 

 of an axial part the pith, which contains air, and of an outer 

 horny part the cortex, in which there is no air. The cortical 

 part is frequently imbricated so as to appear scaly, e.g. bats ; 

 in the sloths it is fluted longitudinally. In some cases the pith 

 predominates, while in others, as in bristles, the horny cortical 

 part is the more important. Two kinds of hairs may be distin- 

 guished according to the nature of the shaft ; contour hairs 

 which are stronger and longer, and woolly hairs which are deli- 

 cate and curled and surround the base of the contour hairs. 

 The woolly hairs constitute the under-fur ; they frequently have 

 the power of cohering (felting) by their rough scaly surface. 

 Hairs 'are usually cylindrical, but sometimes they are flattened ; 

 in the latter case they tend to curl. In some animals the hair is 

 renewed periodically, and in some the hair in winter is longer than 

 and of a different colour from the hair of summer. Smooth mus- 

 cular fibres are often attached to the sheaths of the stronger 

 hairs, by means of which each of them can be moved singly. 

 The bristling of the hairy covering and the erection of the spines 

 over larger extents of surface is caused by the striped muscular 

 system of the dermis. Horny epidermal scales are found in 

 some Edentates (Manis), and occasionally on the under surface 

 of the tails of rodents. The horny scales of armadillos are placed 

 over bony dermal plates. Special cornification of the epidermis 

 is also found over the terminal phalanges of the digits in the 

 form of nails, claws, and hoofs. 



Cutaneous glands. Sweat glands and sebaceous glands 

 (Fig. 257) are widety distributed. Sebaceous glands are almost 

 invariably found opening into the hair-follicle, but they are also 

 found on naked parts of the skin. They secrete a fatty grease 

 which keeps the surface soft and the hair glossy. Sweat glands 

 have the form of coiled glandular tubes with sinuous ducts, and 

 are rarely absent (Cetecea, Mus, Talpa). The larger glands with 

 strongly smelling secretions, which open on various parts of the 

 integument of many mammals are to be regarded as modified 

 sebaceous, or more rarely sweat-glands. As examples of such 

 glands may be mentioned the occipital glands of the camel, the 



