164 



mutual affinities between the great extinct and small existing phyllophagous 

 Unguiculata, at the same time indicates unerringly the true natural affinities of 

 the whole of this great tribe to the other groups of Mammalia. 



It would border upon the ridiculous to advocate the claims of the Mylodon to 

 the Quadrumanous order, because its thorax was wide rather than deep, its 

 muzzle broad and truncated, its pelvis expanded, the head of the radius round 

 and apt for rotation, the inflection of the carpus and tarsus free, the long claws 

 prehensile, and the diet exclusively vegetable. Yet the claims of the Megathe- 

 rians to be associated with the Apes and Lemurs, are, on these grounds, equal 

 with those of the Sloths. 



The only modifications in the small Tardigrades which might mislead a natu- 

 ralist into exaggerating the importance of the characters just cited, are due, in 

 fact, to the absence of characters of the phyllophagous Edentata, by which the 

 Sloths are made inferior to the Megatherioids, without being thereby especially 

 approximated towards the Quadrumana : such, for example, as the removal of 

 the ungulate digits, the loss of the mobility of certain joints in the hands and 

 i'eet, the diminution of the bulk of the body, and the incomplete clavicles in one 

 of the species. 



It is most probable that the Megatherioids, like the Sloths, gave birth to a 

 single and unusually large foetus ; but in that case, they would coincide in their 

 uniparous generation with the Elephant and Whale, as much as with the Ape. 

 If their uterus was undivided, as in the Sloths, they would agree with the 

 Armadillos, as well as with the Quadrumanes. The pectoral mammce of the 

 Dugong and Elephant show the insufficiency of this character in determining the 

 natural affinities of a Mammal, if we assume that the Megatherioids, like the 

 Sloths, resembled the Primates in the position of the lactiferous organs. 



In the lowest of the Quadrumana, as the Mydas Monkey*, the brain, though 

 smooth and almost as devoid of convolutions as in the bird, is yet characterized 

 by the large proportional size of the cerebral hemispheres, which extend a con- 

 siderable way over the cerebellum. In the Sloths the cerebellum is almost left 

 exposed, and in the Megatherioids must have been quite uncovered by the cere- 

 brum, which was of as small proportional size as in the Ant-eaters and other 



* See my paper On the Brains of the Marsupial Animals, Phil. Trans., 1837, pi. v. fig. 2. p. 93. 



