1914] 



Stock: Mylodont Sloths of Rancho La Brea 



325 



for the twelfth nerve are occasionally of unequal size in the same 

 individual and vary somewhat with age. Ventrally the condyles may 

 resemble those in Brown's specimen or may have the proportions 

 seen in the Colorado skull. The marginal ridge of the condyles may 

 vary in distinctness. The distance between the condyles varies as in 

 the South American species. 



MANDIBLE 



The ramus in most of the Rancho La Brea skulls resembles Brown 's 

 specimen and differs from M. garmani in narrowing noticeably in 

 depth from the coronoid process to the front of the first tooth. In 

 no. 21576 the region below the tooth series has more the proportions 

 noted in M. garmani and M. robustus. The anterior end of the 

 symphysis may vary in elevation. In no. 21576 the anterior end is 

 well above the alveolar margin of the first inferior tooth as in M. 

 garmani, while in no. 21156 the end of the symphysis lies almost on 

 a level with the alveolar margin. The symphysial keel varies in size. 

 The greatest width of the predental region across the symphysis is 

 approximately equal to the distance between the first lower teeth in 

 the Rancho La Brea Mylodon, while in Mylodon, robustus the pre- 

 dental width greatly exceeds the distance between the first teeth. The 

 mental foramina are usually two in number on each side, the more 

 anterior being often the larger and showing signs of division. In 

 no. 21578 three foramina occur on one ramus and two foramina on 

 the opposite ramus. 



The posterior internal opening of the dental canal appears always 

 to be of greater width than in M. robustus. The coronoid process is 

 usually rather wide and erect or somewhat recurved. In no. 21578 

 the process is greatly narrowed and slightly overhangs the condyle, 

 the overhang in this case being in part due to a closer proximity of 

 the condyle to the base of the coronoid process. The sigmoid notch 

 may be large and open as in no. 21158 or it may be very small as in 

 no. 21578. The inferior border of the notch may be almost on a level 

 with the dorsal surface of the condyle or it may be well below that 

 surface. The transverse axis of the condyles may be either at right 

 angles to the long axis passing through the symphysis or oblique to 

 that axis. The angle of the jaw may be broad, resembling M. garmani, 

 or more acute as in M. robustus. 



