106 THE VOYAGE OF H.M.S. CHALLENGER. 



Bounding the mesial longitudinal fissure was the sagittal convolution (sac), which 

 commenced at the anterior end of the hemisphere at the posterior limb of the sigmoid 

 gyrus, and then passed back as the marginal convolution of the longitudinal fissure to 

 where the hemispheres diverged from each other, when it inclined outwards to reach the 

 tentorial surface of the hemisphere, though in one specimen it reappeared for a short 

 distance at the posterior border. Between the sagittal and suprasylvian convolutions 

 an intermediate mediolateral convolution (mlc) was placed, which broadened out in front, 

 ascended from the anterior border of the supraorbital area, and then passed backwards 

 to reach the posterior border of the hemisphere, down which it extended behind the 

 suprasylvian convolution. The coronal fissure was a short sulcus, not continuous with 

 either the prsesylvian fissure or the mediolateral fissure, from both of which it was 

 separated by short intermediate gyri. In brain c, where the outer end of the sigmoid 

 gyrus was overlapped by the mediolateral convolution, the coronal fissure was partially 

 concealed by it, and this broad anterior end of the convolution may be called the coronal 

 gyrus. The lateral fissure (I) ran at first upwards and backwards, and then curved 

 downwards to reach the tentorial border of the hemisphere ; it formed the boundary of 

 the suprasylvian convolution in front, above, and behind. The mediolateral convolution 

 was separated from the sagittal convolution by a definite mediolateral fissure (ml) running 

 antero-posteriorly, which almost reached the sigmoid gyrus, but was separated from the 

 coronal fissure by a narrow bridging convolution ; behind it reached the posterior border 

 and tentorial surface of the hemisphere. In the brain drawn in PL X. figs. 1, 3, this 

 fissure was not bridged across, but in the left hemisphere of one of the other specimens 

 a secondary gyrus passed across it about the middle of its length. The sagittal and 

 mediolateral convolutions were wider in front than behind, and formed a larger proportion 

 of the hemisphere anterior to the Sylvian fissure, whilst on the other hand the Sylvian 

 and suprasylvian convolutions were wider behind than in front, and formed much the 

 larger portion of the postsylvian part of the hemisphere. 



The prorean convolution was short, and not beak-like as in the Dog, and was con- 

 cealed by the olfactory bulb. 



The convolutions and sulci on the mesial and tentorial surfaces of the hemisphere 

 were examined after the pons and cerebellum had been removed, and the corpus callosum 

 mesially bisected. In the larger brains the corpus callosum was 50 mm. long, and was 

 distinctly differentiated from the grey surface of the convolution. One of the best 

 marked fissures on these surfaces of the hemisphere was the splenial fissure (sp.) of 

 Krueg. In its general direction it curved behind the splenium of the corpus callosum, 

 from which it was separated by the gyrus hippocampi. It was not quite uniform in its 

 disposition in the two larger brains. 



In the one brain (a) (PL IX. fig. 3) it commenced well forwards on the tentorial 

 surface, and was separated from the postrhinal fissure by two narrow convolutions, which 



