8 GENERAL ANATOMICAL CHARACTERS 



In a large number of mammals hairs of one kind only are 

 scattered pretty evenly over the surface ; but in many there are two 

 kinds, one longer, stiffer, and alone appearing on the surface, and 

 the other shorter, finer, and softer, constituting the under fur, 

 analogous to the down of birds. This under fur, or pashm as it is 

 called by the natives of Kashmir, is especially abundant in the 

 mammals inhabiting the cold plateau of Tibet and the adjacent 

 regions. In many cases hairs of a different character from those of 

 the general surface grow in special regions, forming ridges or tufts 

 on the median dorsal or ventral surface or elsewhere. The tail is 

 very often completed in this way by variously disposed elongated 

 hairs. The margins of the eyelids are almost always furnished with 

 a special row of stifhsh hairs, called cilia or eyelashes ; and in most 

 mammals specially modified hairs, constituting the vibrissa' or 

 whiskers, and endowed, through the abundant nerve supply of their 

 basal papillae, with special tactile powers, grow from the lips and 

 cheeks. In some mammals the hairy covering is partial and limited 

 to particular regions ; in others, as the Hippopotamus and the Sirenia, 

 though scattered over the whole surface, it is extremely short and 

 scanty ; but in none is it reduced to so great an extent as in the 

 Cetacea, in which it is limited to a few small bristles confined to the 

 neighbourhood of the lips and nostrils, and often only present in 

 the young or even foetal condition. 



Some kinds of hairs, as those of the mane and tail of the Horse, 

 appear to persist throughout the life-time of the animal ; but more 

 generally, as in the case of the body hair of the same animal, they 

 are shed and renewed periodically, generally annually. Many 

 mammals have a longer hairy coat in winter, which is shed as 

 summer comes on ; and some few, which inhabit countries covered 

 in winter with snow, as the Arctic Fox, Variable Hare, and Ermine, 

 undergo a complete change of colour in the two seasons, being- 

 white in winter, and gray or brown in summer. The several species 

 of Cape Mole (Chrysochloris), the Desmans or Water Moles (Myogale), 

 and Potarnogale velox, are remarkable as being the only mammals 

 whose hair reflects those iridescent tints so common in the feathers 

 of tropical birds. 



The principal and most obvious purpose of the hairy covering is 

 to protect the skin against external influences, especially cold and 

 damp. Its function in the hairless Cetacea is supplied by the 

 specially modified and thickened layer of adipose tissue beneath the 

 skin, called "blubber." 



Colour. — From the consideration of hair we are easily led to 

 that of colour. As a general rule, bright and primary colours are 

 absent in the class ; but among the Baboons we find brilliant patches 

 of scarlet or blue on some of the bare portions of the body, and one 

 of the South American Monkeys (Brachyums) has its whole face of 



