576 



MAMMALS. 



Ungulata Vera : — Artiodactyla and Perissodactyla. 



In these typical Ungulates, the feet are never plantigrade. 

 In modern types there are never more than four functional 

 toes. The os magnum of the carpus articulates freely with 

 the scaphoid. The brain is well convoluted. The testes 

 descend into a scrotum. The uterus is bicornuate. The 

 placenta is non-deciduate, and either diffuse or cotyledonary. 



Artiodactyla— Pigs, Camels, 

 Chevrotains, and Ruminants. 



Perissodactyla— Tapirs, 

 Rhinoceros, Horses. 



The third and fourth digits of each foot 

 are equally developed, and the line 

 halving the foot runs between them. 



The premolars and molars are usually 

 different. 



There are nineteen dorso-lumbar ver- 

 tebrse. 



The femur has no third trochanter. 



The astragalus has always equal articular 

 facets for the navicular and for the 

 cuboid. The calcaneum has an arti- 

 cular facet for the fibula. 



The stomach tends to be complex, and 

 the caecum is small. 



The mammae are few and inguinal, or 

 numerous and abdominal. 



The placenta is diffuse or cotyledonary. 



The third digit occupies the middle of 

 the foot, is largest, and is symmetrical 

 on itself, so that the line halving the 

 foot bisects the third dig^t. 



The premolars resemble the molars. 



There are almost always twenty-three 

 dorso-lumbar vertebras. 



The femur has a third trochanter. 



The astragalus has a large facet for the 

 navicular, a small facet for the cu- 

 boid. The calcaneum does not arti- 

 culate with the lower end of the 

 fibula. 



The stomach is always simple, and the 

 caecum is large. 



The mammse are always inguinal. 



The placenta is always diffuse. 



Sub-Order Artiodactyla — Even-toed Ungulates. 



Pigs and Hippopotamus (Suina), Camels (Tylopoda), 

 Chevrotains (Tragulina), and Ruminants (Pecora) like 

 Cattle and Deer. 



The general characters of this sub-order have been stated 

 above in contrast to those of Perissodactyla. The equal 

 development of the third and fourth digits, the fact that 

 the premolars have a single lobe while the molars have two, 

 the nature of the ankle bones, the tendency that the stomach 

 has to be complex (as in Camels and Ruminants) are im- 

 portant characteristics. There are others of less obvious 

 importance, such as the absence of the alisphenoid canal 

 which in Perissodactyla encloses the external carotid artery 

 as it passes along the alisphenoid. 



