165 



Edentata. The forward inclination of the occipital plane which the Sloths and 

 Megatherioids present, in common with most other Edentata, is a character 

 manifested by no true quadrumanous animal. 



The dental system has evidently reached its lowest condition, amongst Mam- 

 malia, in the order Edentata. As respects the proportion of the order, com- 

 prising the true Ant-eaters and Pangohns, to which the term ' Edentulata ' was 

 originally and restrictively applied by Brisson, that term is quite appropriate, 

 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 in- 

 cisors ; 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 Edentate species of the Cuvierian system does 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 indi- 

 cation 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 microscopic structure cha- 

 racteristic of the teeth of the Ray and- the Saw-fish *, very different from any 

 modification in the teeth of other Edentata or of other Mammalia. The intimate 

 structure of the teeth of the Megatherioids and Sloths is quite as peculiar to 

 them among Mammalia, but this modification has not been observed in any other 

 class of vertebrate animals. 



This structural peculiarity of the teeth, and their continual growth in the 

 Sloths, are characters which, independently of the total absence of incisors, and 

 diminished number of molars, form an essential objection against their approxi- 

 mation to the Quadrumanous orderf : and the value of these differential cha- 

 racters is greatly increased by their close repetition in the teeth of all the large 



* Report of the British Association, 1838, p. 145. 



t M. de Blainville admits that the character of the dental system — " le systfeme dentaire plus ou 

 moins incomplet," loc. cit. p. 58, — is an indication of their affinity to the Edentata. 



