CHORDATA 



377 



ing of the elephants and a little animal called the Hyrax. 

 Relying on the structure of existing animals, these two groups 

 were long regarded as distinct orders by zoologists ; but within 

 recent years the study of the numerous fossils which have been 

 discovered has revealed a sufficiently close relationship between 

 the two to place them both in the same order. The more 

 striking characteristics may be considered best under the four 

 suborders into which the group is divided. 



Suborder i. Perissodactyla 



The Perissodactyla (Gr. Trepiacros, odd (in number), and 

 MktvXos, finger or toe), or odd-toed Ungulata, are distinguished 

 by the fact that the third digit always forms the axis of the foot ; 

 it may be the only digit developed, or the second and the fourth 

 and sometimes the fifth may also be present (Fig. 369 c and/). 



FlG. 369. Skeleton of the hand of: a, orang-utang; b, dog; c, pig; d, ox; e, tapir; / horse. 

 A, scaphoid; B, semilunar; C, cuneiform; Cc, centrale carpi; D, trapezium; E, tr; 

 zoid; /•; magnum ; G, unciform; M, metacarpus ; /'.pisiform; A', radius ; I', ulna. (From 

 Claus and Sedgwick's Text-book.) 



There is always a good-sized hoof about the end of each digit, 

 the individual walking on the tips of its toes. The mammary 

 glands are always few in number, and the teats are far back 

 on the abdomen ; the testes always lie in a scrotum. There 

 are three types of Perissodactyla, represented by the horse, the 

 tapir, and the rhinoceros. 



