438 ON THE BRAIN OF GREY'S WHALE, 



The greatest breadth of the cerebrum (six inches) is considerably 

 greater than its length (4 \ inches), and in fact exceeds the total 

 length of the encephalon. Its greatest vertical thickness is two 

 inches. It is narrower in front than in Delphinus, and the general 

 shape is more nearly triangular. The convolutions of the upper 

 surface are, as in most Cetacea, highly complex, and arranged in 

 parallel longitudinal folds, but these are better denned than in 

 Delphinus, and their dividing sulci are remarkably deep. There 

 is an inner narrow longitudinal fold thinning off anteriorly ; and 

 external to it three wider ones ; the two inner of these are cut off 

 from one another throughout the greater length of the brain by a 

 deep sulcus, the second and the third are not so deeply divided and 

 are united about the middle of their length by an annectent gyrus 

 which is much broader on the right side than on the left. A fifth 

 fold is traceable, but not so well defined. On the inner surface of the 

 hemispheres the convolutions are arranged in two tiers, the upper 

 very complex with numerous transverse gyri, the lower simpler ; 

 these are separated by a very deep longitudinal sulcus. The 

 convolutions of the orbital and ethmoidal surfaces are chiefly 

 longitudinal. The most remarkable peculiarity of this region, and 

 perhaps of the whole brain, is the great depth of the ectorhinal 

 sulcus, a feature marking off the present form very strongly from 

 Delphinus. The temporo-sphenoidal lobe is marked by numerous 

 short, irregularly arranged convolutions. The apex of the lobe, 

 consisting of two convolutions placed nearly longitudinally, is 

 sharply divided off from the rest by a deep sulcus. The convolu- 

 tions of the tentorial surface follow a radiating arrangement. 



The corpus callosum is an inch and three-eighths in antero- 

 posterior extent. It is thin towards the middle and dilated at 

 either end, more particularly in front where it forms a prominent 

 thickening ; in transverse section it does not appear uniformly 

 curved, but bent at a very obtuse angle a little behind the middle 

 of its length. The lateral ventricles are of very great breath 

 (more than an inch.) The optic thalami are of large extent and 

 cover the greater part of the floor of the ventricles. The anterior 

 cornua of the lateral ventricles do not pass forwards beyond the 



