844 



PHYLUM CHORDATA : CLASS MAMMALIA 



S. and Central America. They are the most arboreal of 

 mammals, passing their whole life among the branches, to 

 which they hang, and along which they move back down- 

 wards. They are solitary, nocturnal, vegetarian animals, 

 sluggish, as their name suggests, and with a very firm grip of 

 life. Their shaggy hides harmonise with the mosses and 

 lichens on the branches, and the protective resemblance is 

 increased by the presence of a green alga on the hair. Their 

 food consists of leaves and shoots and fruits. 

 The body is covered with coarse shaggy hair ; the head is rounded, 

 and bears very small external ears ; the fore-limbs are longer than the 

 hind-limbs, and the two or three digits are bound together by skin, 

 and have long claws ; the tail is rudimentary. 



Concerning the skeleton we may note the rootless, unenamelled, 

 peg-like teeth, the incomplete zygomatic arch with a descending process 

 from the jugal, the presence of clavicles, the rod-like appearance of the 

 embryonic stapes, the occurrence of nine cervical vertebra; in Bradypus, 

 of six in Choloepus. The adult Bradypus has sometimes a separate 

 coracoid or epicoracoid. 



As in most herbivorous animals, the stomach is complex, but there is 

 no caecum. In the limbs the main blood vessels break up into numerous 

 parallel branches. The uterus is simple ; the vagina seems to be 

 originally divided by a median partition ; the placenta is deciduate, and 

 changes in shape during development. One young one is born at a time. 



2. Megatheriidce or Ground Sloths — extinct forms of large size, 



intermediate between the sloths and the ant-eaters. Their 

 remains are found in Pleistocene deposits in N. and S. America. 

 Megatherium exceeded the rhinoceros in size. Near the 

 Megatheriidse the recently exterminated or still living 

 N eomylodon may be included. 



3. Myrmecophagidae — the Ant-eaters, hairy animals, without even 



traces of teeth, with long thread-like protrusible tongue, viscid 

 with the secretion of greatly enlarged submaxillary glands. 

 One form, Myrmecophaga juhata, is terrestrial ; the others, 

 belonging to the genera Tamandua and Cycloturus, are 

 arboreal. All feed on insects. All are Neotropical. The 

 skull is long ; the third finger is greatly developed, the others 

 are small ; the pes has four or five almost equal clawed toes ; 

 the clavicles are rudimentary ; the tail is long and sometimes 

 ]:irehensile. The brain is well convoluted. The uterus is 

 simple ; the placenta is dome-like or discoidal. 



4. Dasypodidae — the Armadillos, all S. American except Tatusia 



novemcincta, which extends as far north as Texas. They are 

 nocturnal, omnivorous animals, able to run and burrow 

 rapidly. They are unique among living Mammals in having a 

 dermal armature of bony scutes united into shields and rings, 

 and covered by horny epidermis. The teeth are numerous, 

 simple, and of persistent growth. Clavicles are well de- 

 veloped. The digits have strong claws or nails. The brain 

 has large olfactory lobes ; the cerebral hemispheres have few 

 convolutions. The tongue is long and protrusible, and the 



