292 THE ANATOMY OF VERTEBRATED ANIMALS. 



The Non-deciduate Mammalia. — I. Ungulata. — A large 

 number of the uon-decicluate Mammalia are conveniently com- 

 prehended under the title of the JJngulata^ though it may be 

 open to question whether the group thus named represents a 

 sing-le order, or more than one. 



In all the Ungulata the placenta is either diffuse, that is to 

 say, the villi are scattered evenly over the surface of the 

 chorion ; or it is cotyledonary, in Avhich latter case, the villi 

 are accumulated in distinct patches on the chorion. These 

 patches are called cotyledons. 



All Ungulata have milk-teeth, succeeded vertically by 

 teeth of the permanent set. The teeth consist of enamel, 

 dentine, and cement, and the grinders have broad crowns, 

 with tuberculated, ridged, or folded enamel. 



Clavicles are never present. The limbs have not more 

 than four complete digits. The ungual phalanges are clothed 

 in obtuse horny sheaths, which are commonly very thick and 

 go by the name of hoofs. Upon these the weight of these 

 quadrupeds is usually supported, whence they have been 

 called unguUgrade. Some few, however, rest the weight of 

 the body upon the under surfaces of the phalanges, or are 

 digitlgrade. The metacarpal and metatarsal bones are elon- 

 gated, and take a vertical, or much inclined position. 



In the female, the mammae are either few in number, when 

 they are inguinal in position; or numerous, when they are dis- 

 posed in two rows along the abdomen. 



The intestine is very generally provided with a csecum of 

 considerable size. 



The cerebral hemispheres always exhibit convolutions, 

 which are usually very numerous ; and, when the brain is 

 viewed from above, the surface of the cerebellum is largely 

 uncovered. 



The Ungulata are divisible into the Perissodactyla and 

 the Artiodactyla^ though it is probable that the attempt to 

 define these groups will break down with the increase of our 

 knowledge of fossil forms. 



1. In the Perissodactyla, the number of the dorso-lumbar 

 vertebra} is not fewer than twenty-two. The third digit of 

 each foot is symmetrical * in itself, and the toes of the hind- 

 foot are odd in number (Fig. 93, B). The femur has a third 

 trochanter (Fig. 100-^). The two facets upon the front face 

 of the astragalus are very unequal ; the less articulating with 

 the cuboid bone. 



* Or at least very nearly so. 



