56o CHORD AT A. 



and most specialised of the Armadillos, known as the Glyptodonts, are 

 extinct forms found in the Pleistocene. The body was enveloped in 

 one huge shield into which the head could be retracted. The vertebral 

 column is ankylosed together, the shield preventing free movement 

 {cf. tortoise). 



From this brief description of the Xenarthra^ it will be 

 seen that the present forms are only the remains of an 

 extensive group of mammals which once held a dominant 

 position in the Neogaean realm. Why such powerful 

 creatures as Megatherium and Glyptodon have disappeared 

 is a question that has puzzled many. All we can say is 

 that a type, like an individual, has a limited part to play on 

 the stage of organic evolution, determined by the relation- 

 ship of an organism to its environment. 



SUB-ORDER II. — NOMARTHRA. 



This small sub-order contains two families which are 

 doubtfully related to each other. They are terrestrial or 

 arboreal and feed on "ants" or termites. Hence in them 

 is found the same elongated snout, small mouth, long 

 mobile tongue and large salivary glands, as in the ant- 

 eaters and Echidna. The uterus is bicornuate, or there 

 are two uteri, and the placenta is non-deciduate and diffuse 

 (or zonary, modified from the diffuse). There are no extra 

 articular processes on the vertebrae. 



Family I. — Orycteropodidae. — Aard-varks or earth pigs. The 

 aard-vark of South Africa is a nocturnal and partially fossorial animal. 

 Its body is sparsely covered with hairs. It is plantigrade with four and 

 five toes all armed with strong claws. The teeth are unique in structure 

 amongst mammals. They grow from persistent pulps, gradually pushing 

 forward in a manner similar to that found in the elephant and the 

 kangaroo. There are usually five on each side in use at the same time 

 and about ten in all. All but the three last are preceded by a milk set, 

 which are absorbed before cutting the gum. This appears to indicate 

 premolars and molars and a possible degeneration from a higher type 

 of heterodont dentition. 



Family II. — Manidse or Pangolins. — The pangolins are elongated, 

 terrestrial, fossorial animals : many can climb trees. They have the 

 body clothed in a series of large overlapping scales of horny epidermic 

 origin. On the under-surface there is usually hair only. The tail is long 

 and protected in a similar manner to the body. Like the Armadillos, 

 they can usually roll themselves into a ball. The skull, especially in the 

 jaw region, is modified for the "termite-eating" habit, as in the anteaters : 



