342 



R. S. Lull — Pleistocene Ground Sloth, 



The occipital condyles in the three Texan specimens vary as 

 much in shape and proportions as either does from the Brea 

 type, and the slightly smaller anterior condyloid foramina, 

 preserved only in No. 10264 of the Texan series, may also be 

 merely an individual variation of no particular moment. 



The inner aspect of the occiput gives an impression of certain 

 elements of the brain. I have before me for comparison casts 

 of the brains of the recent sloths Cholmjnis didactylus and 



Fig. 2. 



Fig. 2. Cast; of the brain of Mylodon harlani, from the Eock Creek 

 specimen No. 10264, Yale collection, and of the modern two-toed sloth, 

 Choloepus didactylus, drawn to scale. One-fourth nat. size. Compare fig. 15. 



C. hoffmanni. That of Mylodon agrees in the superior aspect 

 of the cerebellum with didactylus in the distinct three-lobed 

 character of the surface, though in the fossil form the lobes 

 were more sharply defined and more divergent from the rear 

 forward. The lateral lobes are relatively larger in the recent 

 type. The cerebral impression shows, on the contrary, a some- 

 what greater agreement with 0. hoffmanni in lacking the 

 median longitudinal ridge shown in didactylus and exhibiting, 

 on the contrary, the clear division of the hemispheres. Blood- 

 vessels of the dura mater have impressed themselves deeply 

 into the cranial roof and the convolutions are quite as clearly 

 defined as in the O. hoffmanni brain. The proportions of the 

 brain are much the same in both ancient and modern types, 

 despite the difference in cranial proportions, the elongation of 

 the skull in Mylodon including in general the portion anterior 

 to the brain case — procerebral dolichocephaly. 



Squamosals. — Three squamosal bones are preserved, two 

 from the right side and a less complete one from the left. 

 The right ones I have referred to Nos. 10265 and 10266 re- 



