CHAEACTERS OF ODD-TOED HOOFED BEASTS. 169 



tent : its base is perforated by the ectocarotid canal. The 

 entopterygoids are thin plates, applied like splints over 

 the inner side of the squamous suture between the ptery- 

 goid processes of the palatines and alisphenoids. The 

 postglenoid process in the horse is less developed than in 

 the tapir. The Eustachian process is long and styliform. 

 There is an anterior condyloid foramen, and a wide 

 "fissura lacera." The broad and convex bases of the 

 nasals articulate with the frontals a little behind the an- 

 terior boundary of the orbits. The space between the 

 incisors and molars is of greater extent than in the tapir; 

 a long diastema is not, however, peculiar to the horse ; 

 and, although it allows the application of the bit, that 

 application depends rather upon the general ^ature of the 

 horse, and its consequent susceptibility to be broken in, 

 than upon a particular structure which it possesses in 

 common with the ruminants and some other herbivora. 



The tapir and the rock cony have four digits on each 

 fore-foot, and three digits on each hind-foot; but they 

 resemble more the horse and rhinoceros than any other 

 TJngulata, If the osteological characters of the hoofed 

 animals with the hind digits in uneven number be com- 

 pared together, they will be found to present, notwith- 

 standing the differences of form, proportion, and size 

 presented by the rhinoceros, hyrax, tapir, and horse, the 

 following points of agreement, which are the more sig- 

 nificative of natural affinity when contrasted with the 

 skeletons of the hoofed animals with digits in even num- 

 ber. Thus, in the odd-toed or " perissodactyle" ungulates, 

 the dorso-lumbar vertebroB differ in different species, but 

 are never fewer than twenty-two ; the femur has a third 

 trochanter, and the medullary artery does not penetrate 

 the fore part of its shaft. The fore part of the astragalus 

 15 



