HIGH SCHOOL ZOOLOGY. 



IG-i 



Ocean (IfaUcore, Fig. 113), but the latter lias tusk-like incisors 

 in the upper jaw, which are only transitorily present in 

 the manatee. The caudal fin of the latter is by no means so 

 effective a propelling organ as is that of the dugong, which 

 creature is, on the other hand, quite helpless on land. "While 

 the skin in the sea-cow was exti-emely thick and hairless, that 

 of the manatee is covered with stiff bristles, which are both 

 fewer in number and shorter in the dugong. Some fossil 



Fig. 113.— Duffong (Halicore.) ^ 



members of the order are known, in which both the teeth and 

 the skeleton of the hind limbs are more completely represented 

 than in the living Sirenia, but these, instead of uniting the 

 group to the Cetacea, rather pi'ove an alliance with the hoofed 

 animals, to the study of which we now proceed. 



23. The remaining orders of Mammalia arrange themselves 

 naturally in two series, the Hoofed Animals (Ungulata) on the 

 one hand, those provided with claws and nails on the other 

 (Unguiculata). Although, at first sight, this distinction appeai-s 

 to be of little importance, the hoof being a horny covering for 

 the whole of the distal joint of a toe, while the claw or nail is 

 merely developed on one surface (the anterior), yet it is the 

 mark of a difference of function which is associated with some 

 of the most characteristic peculiarities of the Ungulata. In by 

 far the greater number of the living hoofed animals the extrem- 

 ities are devoted entirely to the function of locomotion, and in 

 most cases the number of toes is i-educed in accordance with a 



