22 



ZOOLOGY. 



with milk-glands on the thorax or abdomen, or both 

 those regions. 



Speaking quite broadly, the skeleton is like that of 

 man, described on pp. 4-8. There are, however, great 

 differences in detail. The cranium is relatively much 

 smaller, and the bones of the face (especially of the 

 jaws) are usually much larger than in the human skull. 

 The number of the cervical vertebrae is seven in all 

 Mammals, as in man ; but the other kinds of vertebrae 

 vary in number in the different species. The number 

 of caudal vertebrae, for example, is very variable. As 

 most Mammals go on all fours, their fore and hind 

 limbs are much more similar than is the case in man. 

 In many the thigh and upper-arm bones are drawn 

 closely up to the body (horse, ox, pig). Mammals 

 never have more .than five fingers or toes, but may 

 have fewer. The thumb or great toe is the first to 

 disappear (hind foot of dog, fore and hind foot of 

 pig). There may be only three (rhinoceros), two (ox. 



Fig. 12.— Vertical Section of 

 a Human Grinding Tootll. 



Fig. 13. — Crown of a Grinder of tlie Ox. a, 

 cement; b, enamel; c, dentine ; d, enamel; 

 e, cement. 



sheep), or one (horse) digit developed. In addition to 

 fully developed digits, there are in many Mammals 

 very small stunted ones (" dew-claws" of the stag). 



There are also great differences in the way of 

 resting the feet on the ground. Man and bear tread 

 on the soles of the feet (plantigrade) ; dog and cat 

 walk on the under side of the toes (digitigrade), not 

 on the other parts of the feet. Ox, pig, horse, etc., 



