XENARTHRA. 727 



Order XENARTHRA. 



1. Bradypodicke Sloths. The three-toed sloths (Bradypits} and the 



two-toed sloths (Choltxpus] are restricted to the forests of 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 downwards. 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 Cholcepus (but see p. 670). The adult Bradypns has some- 

 times 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 origin- 

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

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



2. Megatheriida; 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 Mega- 

 theriidas the recently exterminated or still living Neoinylodon 

 may be included. 



3. Myrmecophagidit the Ant-eaters, hairy animals, without even 



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

 with the secretion of greatly enlarged submaxillaiy glands. 

 One form, Mynnccophaga jubata, is terrestrial, the others, 

 belonging to the genera Tamandua and Cyclotunis, 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 

 prehensile. The brain is well convoluted. The uterus is 

 simple : the placenta is dome-like or discoidal. 



4. Dasypodidre 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 developed. The 



