20 CHORDATE ANATOMY 



Order 6. Perissodactyla. The perissodactyls usually have an 

 uneven number of hoofs on each foot. They include the horse, ass, zebra, 

 tapir, and rhinoceros. The third toe is the largest and the only one func- 

 tional in the horse. The enamel of the back teeth is complexly folded. 



Order 7. Subungulata. Hoofed forms usually with plantigrade 

 feet. Subungulates are the elephants and mastodons, and the hyrax or 

 cony. The proboscidians such as the elephants have on each foot five toes 

 on which they walk. Their testes do not descend into a scrotum. Sireni- 

 ans (Manatee and Dugong) are a suborder of this group. 



Order 8. Cetacea. The cetaceans include whales, porpoises and 

 dolphins. They are aquatic mammals with fish-like bodies. Hairs and 



LEMUR CATTA. 



Fig. 23. — Lemur, a primitive Primate. (Redrawn after Shipley and McBride.) 



pelvic extremities are absent in the adult. There are two abdominal 

 teats. Teeth may be replaced by whalebone. 



Order 9. Chiroptera. Chiroptera are the bats and flying foxes. 

 Their anterior limbs are modified to support the wings, the fingers are 

 joined by a web, and the sternum has a keel. 



Order 10. primates. The primates include lemurs, marmosets, 

 monkeys, baboons, apes, and men. They are mostly arboreal in habit. 

 Nearly all have five digits with flattened nails, and in aU except the lowest 

 forms the thumb is freely opposable to the fingers. Mammary glands 

 are usually a single pair and thoracic. 



Primates are divided into two sub-orders. 



Sub-order Lemuroidea. The lemuroids include the lemurs and 

 tarsiers. They are arboreal and nocturnal, small and not especially 

 monkey-like. Typical lemurs have a claw on the second digit of the 



