NERVOUS SYSTEM. VEBTEBBATA. 



279 



One of the most distinctive features of the brain of the 

 Bear is the nature of the crucial sulcus. This sulcus is of 

 great length and depth and is almost wholly confined to 

 the dorsal surface of the hemisphere (figs. 155 & 156), 

 upon which it pursues an oblique course and is placed 

 relatively far back on the hemisphere. After examining 

 such a brain as this, we can readily appreciate the fact that 

 tliis sulcus is the only one in the Carnivore which can, in 

 any sense, be regarded as the representative of the sulcus 

 of Rolando of the Primate brain. [Compare the crucial and 

 precrucial sulci of a Bear (say D. 365) with the central and 

 superior precentral sulci of a Gorilla (say D. 661).] 



Fig. 156. (x.) 



SULC .VERT. 

 SULC. CRU. 



3ULC. INTERCAL. 



S'JLC.ROS 



-SULC. P. CALC. 



SULC. CALC. 

 SULC.PARACALC, 



HIP. ft 

 SULC. URS.(JOININS CALC.) 



On the right hemisphere there is a deep, long, precrucial 

 sulcus proceeding forward from the crucial, and distinctly 

 mapping out the right lateral boundary of Mivart's " Ursine 

 lozenge" (fig. 155); but on the left side the sulcus is much 

 smaller and is supplemented by a larger " complementary 

 precrucial/' which is quite independent of the crucial 

 sulcus. 



Although precrucial sulci may make their appearance 

 among the larger representatives of other families of the 

 Carnivora, such, for instance, as the Lion and Hysena, yet 

 the presence of these sulci and the " Ursine lozenge," 

 which they map out, is a valuable distinctive feature of the 



