45 



concomitant depth of the jaws, are features of resemblance to the maxillary and dental 

 characters of the Elephant; but the fundamental structure of the teeth, not only of 

 the Megatherium, but of all its extinct congeners, is manifested in the present day 

 exclusively by the restricted and diminutive family of the Bradypodidce. I conclude, 

 therefore, the present section of this memoir by repeating the remark which I was 

 led to make in a former memoir*, relative to the existing Sloths : — " These Mammals 

 present to the zoologist, conversant only with living species, a singular exception in 

 their dental characters to the rest of their class ; but there has been a time when 

 this peculiar dentition was manifested under as various modifications as may now be 

 traced in some of the more common dental types in existing orders of Mammalia." 



Comparative Table of Dimensions of the Skull of the Megathere, Mylodon, and 



SCEU DOTH ERE. 



Megatherium 

 Americanum. 



Mylodon 

 robustus. 



Scelidotherium 

 leptocephalum. 



Cranium. 

 Length from the occipital condyles to the fore-end of the upper 



jaw 



Length from the occipital condyles to the fore-part of the 



malar bone 



Length from the fore-part of the malar bone to the fore-end 



of the upper jaw 



Breadth across the widest part of the zygomatic arches 



Least breadth at the interspace of those arches 



Breadth of the fore-part of the nasal bones 



Mandible. 



Length 



Breadth between the hinder ends (angles) of the rami 



Breadth between the condyles 



Breadth between the posterior sockets of the teeth 



Breadth between the anterior sockets of the teeth 



Breadth across the fore-part of the symphysis 



Depth of ascending ramus from the upper part of the condyle 

 Depth of ascending ramus at the fore-part of the base of the 



coronoid process 



Depth of horizontal ramus at the fore-part of the first socket 



Length of the symphysis following the outer curve 



Fore and aft extent of base of coronoid process 



From the back part of the condyle to the end of the angular 



process 



From the end of the angular process to the last socket 



From the first socket to the anterior margin of the jaw , 



Extent of the alveolar series 



Breadth of the condyle 



ft. in. tin. 



2 7 



1 8 



10 6 



6 



4 6 



9 



8 



1 1 

 9 



ft. in. tin. 



1 6 6 

 1 2 



5 

 10 

 5 

 3 



1 3 6 



6 3 



4 2 



2 10 



4 



5 4 



5 7 



3 7 



3 



4 3 



3 8 



3 2 



6 6 



3 6 



5 4 



2 6 



ft. in. tin. 



1 8 4 



11 6 



8 8 



7 



3 7 



2 8 



1 6 



4 



1 



1 



1 



2 



5 



o 







7 10 



4 4 



1 10 



§ 7- Of the Bones of the interior Extremity. 



The bones of the limbs of the Megatherium are not less fraught with interest to 

 the comparative anatomist and physiologist than are those of the trunk and head, 

 by reason of their peculiar proportions and configurations, and, more especially, 

 as the unguiculate type on which they are constructed is exemplified in a quadruped 

 of such enormous bulk. The anterior extremities exceed the posterior ones in 



* On the Mylodon robustus, 4to, p. 45. 

 G 



