HAIR. 619 



hair from the hot sand of the desert. 1 Nocturnal quadrupeds of 

 hot climates, as, e.g., Lemuridce, have the soft fur and the longer 

 scantier kind of hair. The northern Wild Boar has an undercoat 

 of fur besides the bristles : in most domestic Hogs the latter alone 

 are developed ; and a gland-like body partly surrounds the matrix 

 of the bristle, fig. 485, i. Rhinoceroses and Elephants of tropical 

 latitudes have but one kind of hair, most conspicuous in the 

 young, especially in elevated localities, but almost wholly lost in 

 the full-grown animal. The Hippopotamus, Sirenia, Cetacea, 

 Bimana, are examples of naked Mammals ; but on the limited 

 localities where the skin develops such a covering, it is of the 

 mammalian character — hair or bristle. The foetal Whales show 

 the latter on the lip, the adult Elephants and Rhinoceroses on the 

 tail. Human hair, which continues to grow through more or less 

 of life, has distinctions as to localities and length, characteristic 

 of age and sex : it varies in colour from pale yellow to black, and 

 in form from straight to crisp, resembling wool on the head of 

 the Negro variety. 



The degree of imbrication of the scaly outer layer of the human 

 hair is such that rubbing one between the thumb and finger pushes 

 the root-end away. Beneath the scales the cortical part of the 

 hair is minutely fibrous ; it includes a cellular pith with pigment, 

 upon which the colour of the hair mainly depends. In the minute 

 hairs on the general surface of the body, the pith is wanting. 

 I have observed the hair of the beard to be three-sided, with 

 rounded angles, in transverse section ; the hair of the head of the 

 same individual being a full oval in such section. 



The general direction of the minute and fine hairs on the 

 human limbs accords with that of the medullary arteries of 

 the long bones, viz. toward the elbow-joint and from the knee- 

 joint. 2 A corresponding disposition prevails in the hairy clothing 

 of the limbs of Quadrumana. In the attitude assumed by an 

 Ape crouching beneath the pelting of a tropical shower, with 

 close-bent limbs, thigh and fore-arm upward, arm and leg down- 

 ward, the reverse directions of the hairs on the proximal and 

 distal segments will be seen to be such as to act in both as a 

 downward watershed. 



The general direction of the hair in swift quadrupeds offers 

 least impediment to forward motion. Some small burrowers, 

 which move backward as well as forward in their long and narrow 



1 xx. vol. iii. p. 243. 



2 Eschricht has given ample details of the disposition of the hair in the human 

 foetus, in ccxxx". 



