RODENTIA. 553 



"thick subjacent layer of fat. The amount of hair on the skin varies greatly, 

 but appears to decrease in proportion to the domesticity of the animal, the 

 wild boar being provided with a comparatively thick coat. The hairs are 

 thick and strong, being commonly known as bristles.- In a general sense the 

 hoofs resemble in form those of the ruminant, but they consist of four 

 pieces on each extremity. See Fig. 32. 



CAENIVOEA. 



The conchal cartilage in the dog is extremely variable, both in shape and 

 size, according to the breed, but in most breeds it folds downwards, forming 

 the drop, or flap, which serves to protect the cavity cf the external ear from 

 the intrusion of foreign matters. In the cat, and in fact in the felidce 

 generally, the concha is broad, short, and erect, with the opening turned 

 forwards. 



The globe of the eye is much more spherical, while the iris is of various 

 modified shades of yellow. The pupil is circular, and the tapetum lucidum 

 of a bluish white. In .some features the eye of the cat differs, the pupil being 

 circular only when fully dilated ; when contracted it appears as a narrow 

 vertical slit ; the iris has a greenish lustre, while the tapetum lucidum is 

 golden yellow. 



The sudoriferous glands are extremely minute and difficult to find, excepting 

 about the region of the nose and digital pads. The latter are callous thicken- 

 ings of the epidermis, upon which the animal walks. The distal phalanges 

 are covered by horn, which projects, curving outwards and downwards to form 

 the claws. As we have already seen, the claws are retractile in the cat, where 

 they are also sharp, and serve chiefly as weapons of ofi"ence. ' In the dog the 

 •claws are virtually fixed and blunt, becomiug worn by constant locomotion 

 .and scratching. 



No rule can be given as to the nature of the hair in dogs,. as it differs greatly 

 in length, texture, and colour. In the cat it is short, sleek, and furry, and in 

 colour equally variable. The touch-hairs, or whiskers, situated at the sides of 

 the nose, are well marked in the cat, and are usually white in hue ; the tail is 

 generally covered by hai'" nearly as short as that on the rest of the body. 



KODENTIA. 



The concha of the ear is large and very long in the rabbit, and may be either 

 •erect or pendent, but most usually it is the former. There are no puncta 

 lachrymalia J the lachrymal gland and membrana nic(;itans are both large. 

 The rabbit tribe is remarkable for including a large number of albinos or 

 individuals devoid of pigmentary tissue ; the result of this is perfect whiteness 

 of hair and skin, apd redness of the iris, the latter being due to the thick plexus 

 of blood-vessels contained therein, which is displayed by the absence of 

 pigment. 



The claws somewhat resemble those of the dog, but they are better adapted 

 for scraping the soil, the animal being naturally a burrower. 



