THE ANIMAL KINGDOM 455 



Examples: Didelphys virginiana, the Virginia opossum; 

 Macropus giganteus, the giant kangaroo of Australia. 



SUBCLASS 3. EUTHERIA. Placental mammals. The 

 vagina is single and the embryo is nourished by a placenta 

 formed from the allantois of the embryo and the lining of the 

 uterus. The allantois is an embryonic membrane. Eutheria 

 are called placental mammals, but as a matter of fact a placenta 

 is also present in some marsupials. 



Section A. Omnivorous Forms. Five digits on hand and foot ; 

 clavicle well developed. 



Order 1. Insectivora. Typically, walking feet with dorsal sur- 

 face often scaly; first digit not opposable; radius and ulna 

 separate, but tibia and fibula often fused. 



Examples: European hedgehog, shrews, and moles. 



Order 2. Primates. Primitive dentition; first digit opposa- 

 ble on fore or hind limb or both ; hands and feet for grasping. 

 Large cranium; reduced jaws and nasal cavities; orbits directed 

 forward. Semierect or erect posture. 

 Examples: Monkeys, apes, and Man. 



Order 3. Rodentia. Two chisel-shaped incisor teeth (four in 

 rabbits) in each jaw, modified for gnawing. Radius and ulna 

 separate; tibia and fibula some times fused. Clavicle absent 

 in guinea pigs. 



Examples: Mice, rats, rabbits, guinea pigs, beavers, and 

 porcupines. 



Order 4. Galeopithecoidea (Dermoptera). On each side a 

 lateral fold of skin including limbs and tail, when spread acts as 

 a parachute, enabling the animal to make long leaps. Primi- 

 tive dentition. Ulna, fibula, and clavicle rudimentary. 



Example: Galeopithecus, the flying lemur of India and the 

 Malay Archipelago, the only representative of the order. 



Order 5. Chiroptera. Greatly lengthened arm bones and fingers 

 supporting a membranous wing used in flying. 

 Example: Bats. 



Order 6. Edentata. Incisors and occasionally all of the teeth 

 lacking. 



Examples: Anteaters, sloths and armadillos. 



Order 7. Tubulidentata. Body covered with bristlelike hairs; 

 five prismatic molars in each jaw; four toes in front, five 

 behind. 



