'220 PHYSIOLOGICAL SERIES. 



dorsal edge of the hemisphere in a manner curiously like 

 the conjoint crucial and intercalary sulci of many Carni- 

 vores, such as the Civet. [Figure 93 does not represent this 

 specimen.] 



The corpus callosum (c.c.) and psalterium (p.s.) are 

 relatively short and of a somewhat simple type (fig. 90), 

 and the relations of the hippocampus to the commissures 

 and to the supracallosal (V.H.) and precallosal (v.ii/) 

 vestiges of the hippooampal arc are clearly shown. 



The posterior quadrigeminal bodies are more prominent 

 than the anterior pair, and the mesial (posterior) geniculate 

 body on each side is so large as to appear like a lar^e caudal 

 projection of the chief mass of the optic thalamus. It 

 touches the cerebellum posteriorly. These features are some 

 of the physical expressions of a highly acute sense of hearing. 



The cerebellum resembles that of Bradypus but is con- 

 siderably larger (figs. 92 and 94). 



The large paraflocculus is seen to great advantage. 



Elliot Smith, Trans. Linn. Soc. vol. vii. 1899, p. 309. 



D. 276. The brain of a Two-toed Sloth (Cholcepus didactyln*) 

 (fig. 92). 



In this brain the chief sulcus in the region where the 

 " lateral " sulcus should be found obviously corresponds to 

 that which in the last specimen was called " entolateral/ 1 

 There is, however, a coronal sulcus like that of Bradypus 

 (D. 273), occupying the situation of the anterior part of the 

 "lateral" sulcus of the last specimen; and also a >hort 

 caudal sulcus on the lateral side of the " entolateral " whieh 

 appears to join the calcurine. 



This shows to how great an extent this group of sulci 

 lacks morphological stability. They accommodate them- 

 selves to slight mechanical differences in the proe< 

 growtli in Mich a way that no exact homology with appa- 

 rently identical sulci in other groups can be said to exi>t. 



0. C. l'6-2:\\\. 



D. 277. A cast of the cninial cavity of a Two-toed Sloth 

 (Clwlcepus didactylus). 



This shows the exact shape and size of the cerebellum, 



