356 Zoological Sumniari/ of Extinct and Living Animals 



mammal, if we assume that the Megatherioids, like the Sloth, 

 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 considerable 

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

 left exposed, and in the Megatherioids must have been quite 

 uncovered by the cerebrum, which was of as small proportional 

 size as in the Ant-eaters and other Edentata. The forward 

 inclination of the occipital plane which the Sloths and Mega- 

 therioids present, in common with most other Edentata, is a 

 character manifested by no true quadrumanous animal. 



The dental system has evidently reached its lowest condi- 

 tion, amongst Mammalia, in the order Edentata. As respects 

 the proportion of the order, comprising the true Ant-eaters 

 and Pangolins, to which the term " Edentulata" was originally 

 and restrictively applied by Brisson, that term is quite appro- 

 priate, and it would have been well if its signification had not 

 been extended to so many species to which it is inapplicable. 

 The Orycterope, or Cape Ant-eater, for example, has molar 

 teeth ; some of the Armadillos possess, in addition to their 

 molars, one or two teeth, which may, from their position, be 

 termed incisors ; and the two -toed Sloth has teeth which, by 

 their size and shape, merit the name of canines ; but whatever 

 be the position, shape, or use of the teeth, in no Edentata 

 species of the Cuvierian system does the enamel enter into their 

 composition. 



The modifications in the intimate structure of the teeth, 

 which are extreme, and peculiar to the quadrupeds of this order, 

 may be regarded as another indication of the low ebb to which 

 the development of the dental character has sunk, now variable, 

 and, as it were, flickering before its final disappearance. 



In the Orycterope we find, strangely repeated, a microsco- 

 pic structure characteristic of the teeth of the Ray and Saw- 



* See my paper on the Brains of the Marsupial Animals, PhiU Trans., 1837, 

 PI. v., Fig. 2, p. 03. 



