NERVOUS SYSTEM. VERTEBRATA. 



353 



On the mesial surface, which is of unusually great area, 

 there is a sulcus (fig. 202, 5) of extraordinary depth, which 

 pursues most of its course on the mesial surface near the 

 rounded dorsal margin ; both of its extremities cross on to 

 the cranial aspect. If this sulcus does not represent the 

 lateral it must be an unusually accentuated entolateral 

 sulcus, such as occurs in the Seals. 



The calcarine sulcus is very deep and is placed very 

 close to the splenium of the corpus callosum. It is joined 



Fig. 202. (xf) 



CORP. CALL 



SULC.INTERCAL. 



SULC.GEN. - 



...-SULC. CALC. 



LAM. TERM. 



OPT. CHIAS 



to the intercalary and genual sulci to form a complete 

 cingular arc (fig. 202). The wide gap between the latter 

 and sulcus 5 contains innumerable sulci, three of which 

 are very pronounced posteriorly (fig. 202, 6). 



The orbital sulcus is represented by two or three rela- 

 tively insignificant furrows on the basal surface. It is 

 possible that the dwindling o the olfactory regions accounts 

 for the insignificance of the orbital sulcus. 0. C. 1333 I. 

 Presented by the Westminster Aquarium. 



D. 516. The brain of a Dolphin (Delphinus tursio) . 0. C. 1 333 E. 



D. 517. The brain o a Dolphin (Delphinus sp.). O. C. 1333 o. 

 VOL. ii. 2 A 



