45 



rior articular processes, in this vertebra, send upwards a ridge from along 

 nearly the middle surface, towards the anterior part of the transverse 

 process. 



The dorsal vertebrae of the Megatherium very closely resemble those 

 of the Mylodon, subsequently to be described ; but the spines of the 

 anterior ones are relatively longer, in relation to the relatively larger 

 and heavier head. They are equally remarkable, with those of the My- 

 lodon, for the capacity of the spinal canal, the expanded arches of which 

 similarly overlap each other, and are articulated by broad, flat, and nearly 

 horizontal surfaces : the only difference deserving notice in the dorsal 

 vertebrae of the Megatherium is this, that through a great proportion of 

 the posterior part of the dorsal region there is a third articular surface 

 on both the front and back parts of the imbricated neural arches : the 

 anterior surface is situated on the anterior part of the base of the spine, 

 between the two normal articular processes ; the posterior median surface 

 is supported on an osseous platform, depending from the posterior and 

 under part of the root of the spine. 



256. The body of the last lumbar vertebra : it is characterized by the flatness 

 of its posterior surface. 



257- The pelvis of the Megatherium. 



This is the most striking feature in the skeleton of the present gigantic 

 extinct Sloth : it consists of five sacral vertebrae, anchylosed to each other 

 and to both the iliac and ischial bones. The latter are united to the ex- 

 tremities of the transverse processes of the last two sacral vertebrae, which 

 are unusually thick and strong ; the great ischiadic notch is thus con- 

 verted into a foramen, as in the pelvis of the existing Edentate qua- 

 drupeds. Among these the Sloths alone resemble the Megatherium in 

 the expansion of the iliac bones, but this character is more marked in 

 the Megatherium than in the Elephant, and is associated with a much 

 greater proportionate size of the pelvis : the extreme breadth of the pelvis 

 in the large Asiatic Elephant is three feet, eight inches, whilst in the 

 Megatherium it is upwards of five feet. The spines of the four anterior 

 sacral vertebrae are confluent at their base ; their summits, which are re- 



