474 



ZOOLOGY 



SECT. 



J7/ 



Systematic Position of the Example. 



The genus Lepus, to which the common Rabbit belongs, com- 

 prises a number of other species, the common Hare being among 

 the number, distinguished from one another by slight differences 

 in the proportions of the parts and in other general features. Lepus 

 is the only genus of the family Leporidce, which is associated with 

 the family Lagomyidce or Picas under the designation Duplici- 

 dentata, owing to the presence in these two families, and in these 

 two alone of the entire order Rodentia to which they belong, of a 

 second pair of incisors in the upper jaw. The chief distinctive 

 features of the family Leporidse are the elongated hind-limbs, the 

 short recurved tail, the long ears, and the incomplete clavicles. 



3. GENERAL ORGANISATION. 



Integument and General External Features. Nearly all 

 Mammals are covered with hairs (Fig. 1111) developed in hair- 

 follicles. Each hair (Fig. 

 1112) is a slender rod, and 

 is composed of two parts, 

 a central part or pith (M) 

 containing air, and an 

 outer more solid part or 

 cortex (R) in which air 

 does not occur ; its outer- 

 most layer may form a 

 definite cuticle (0). Com- 

 monly the cortical part 

 presents transverse ridges 

 so as to appear scaly. In 

 one case only, viz., Sloths, 

 is the hair fluted longi- 

 tudinally. The presence 

 of processes on the surface, 

 by which the hairs when 

 twisted together interlock 

 firmly, gives a special 

 quality to certain kinds 

 of hair (wool) used for 

 clothing the felting quality as it is termed. A hair is usually 

 cylindrical ; but there are many exceptions : in some it is com- 

 pressed at the extremity, in others it is compressed through- 

 out ; the latter condition is observable in the hair of negroid races 

 of men. The fur is usually composed entirely of one kind of hair ; 

 but in some cases there are two kinds, the hairs of the one sort very 

 numerous and forming the soft fur, and those of the other consisting 

 of longer and coarser hairs scattered over the surface. Examples 



SM 



FIG. 1111. Section of human skin. Co, dermis ; D, 

 sebaceous glands ; F, fat in dermis ; G, vessols in 

 dermis ; GP, vascular papillae ; H. hair ; a. nerves in 

 dermis ; NP. nervous papillae ; Se, horny layer of 

 epidermis ; SD, sweat-gland ; SD*, duct of sweat- 

 gland ; SM, Malpighian layer. (From Wiedersheim's 

 Comparative Anatomy.) 



