NERVOUS SYSTEM. VERTEBRATA. 277 



pyriform lobes phenomena directly associated with the 

 aquatic mode of life of the Otter. 



The typical Arctoid plan of the sulci can be distinctly 

 recognised. Note especially that the crucial sulci are 

 placed very far forward and have well-marked precrucial 

 branches. 



Mivart, Journ. Linn. Soc., vol. xix. 1886, p. 20. 



Family UKSID^E. 



D. 360. The brain of a Polar Bear ( Ursus maritimus), ( $ ), from 

 which the left hemisphere has been separated. 



The "Sylvian fissure" is distinguished by its great 

 length and depth, and as a result the suprasylvian and 

 corono-lateral arcs which are grouped around it become 

 greatly elongated and acutely flexed. 



Fig. 154. (Reversed, xf.) 



SULC.LAT. 



SULC.P.CAUD. 



I** ARCU. QYR. \ SULC.P. LAT. PARAFLOC. 



SULC.P. SYL 



Sir William Turner long ago pointed out that the whole 

 of the first arcuate gyrus of Leuret is hidden in the depths 

 of this deep a Sylvian fissure." On the right hemisphere 

 (fig. 154) a considerable portion of the second arcuate 

 gyrus (from which the lips of the fissure are formed) has 

 been cut away so as to expose this buried gyrus. It will 

 be seen to be acutely flexed around a long sulcus, which 



