620 ANATOMY OF VERTEBRATES. 



tunnels, would be inconvenienced by such unchangeable disposi- 

 tion of their fur. Accordingly in Moles, Shrews, and Platypi, 

 e.g., the stem of the hair is filamentary, the end broad and flat, 

 and the slender and expanded parts may alternate twice or 

 oftener in the course of the hair, enabling the whole fur to 

 assume any direction in which it may be stroked. 



The heat-retaining property of the pilose covering is mainly 

 due to the amount of air it is able to retain. The long curly 

 character of the Sheep's and Llama's fleece is one modification to 

 this end ; the swifter Deer and Antelope are not so encumbered ; 

 but the hairs composing their thin but close and smooth pelt 

 have a cellular structure which combines lightness with the re- 

 qui site air-intercepting quality. 



In the Horse there is a central point on each flank, whence 

 the hair radiates in a somewhat spiral manner: the corresponding 

 centre in the Giraffe is a little behind the middle of the abdomen, 

 towards the lower part. 1 



The hide of the larger Ruminants which are exposed to the 

 elements in the prolonged act of grazing is defended by the 

 greasiness of the hair, as may be felt in the recently killed Red- 

 deer or Fallow-deer. The amount of sebaceous matter excreted 

 with the hair in some Antelopes is such as to have suggested a 

 specific name in accordance therewith. 2 



The varieties of structure of hair are extreme : those of Deer 

 seem almost wholly to consist of cellular pith, the cortex unde- 

 finable : the tail-hair of the Horse, and the Pig's bristle, offer 

 the opposite extreme of thickness of cortex and minimum of pith. 

 But these and other modifications demand a special micrography. 3 

 Hairs of some quadrupeds, the Racoon, e.g., in the filamentary 

 productions of the cortical scales, recall the character of the 

 immature down in Birds (vol. ii. p. 237). In some Rodents, the 

 Hare, e.g., several fine hairs project from the mouth of the same 

 sheath as the larger hair. In Mice and Shrews the margins of 

 the cortical scales encompass the hair and project forward or 

 rootward. This free projection is such in some bats that the 

 hair presents the appearance of a succession of ensheathed 

 funnels with their apices backward or outward. The hair of the 

 Sloth is fluted, the crust appearing to be composed of several 



1 The varieties in this respect merit more notice than they have hitherto received. 



2 Laurillard's AntUope unctuosa is probably the same species as Kobus Sing-sing of 

 Ogilby. 



3 Brief immersion in sulphuric acid and cleansing with ether are requisite prelimi- 

 naries for clear and satisfactory microscopic specimens of hairs. 



