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



The convolution which was placed immediately to the outer side of the sagittal con- 

 volution was the mediolateral or 2nd external convolution (mlc). It extended forward to 

 the coronal fissure where it formed a tortuous fold — the coronal gyms ; on the vertex it 

 was narrow, but as it passed backwards it formed a broad tortuous convolution, subdivided 

 by sulci, which assisted the sagittal convolution in forming the posterior boundary of 

 the hemisphere. Between the mediolateral and sagittal convolutions was the medio- 

 lateral fissure (ml); it was not continuous with the coronal fissure iu either hemisphere, 

 and on the right side both it and the sagittal and suprasylvian convolutions were so 

 pushed inwards by the highly tortuous suprasylvian convolution, that it approached 

 close to the mesial longitudinal fissure. 



The corpus callosum and the other mesial structures in the cerebrum were then 

 divided longitudinally, and the pons and cerebellum were removed by cutting through 

 the crura cerebri. The convolutions and sulci on the mesial and tentorial surfaces were 

 thus exposed, and the following arrangement was recognised. The corpus callosum (ccl) was 

 44 mm. long ; posteriorly it had a rounded free end or splenium, whilst anteriorly it bent 

 down to the base of the brain to form the genu ; it could be easily torn up into trans- 

 verse fasciculi of nerve fibres. A septum lucidum occupied the hollow of the genu 

 between it and the fornix. The splenial fissure (sp), Krueg, was well marked. It com- 

 menced immediately behind the lobus hippocampi and curved backwards, upwards, and 

 then forwards behind the splenium, from which it was separated by the gyrus hippocampi ; 

 it then ran forwards above the corpus callosum, but separated from it by the callosal 

 convolution, and was continuous at the anterior end of the hemisphere with the crucial 

 fissure. It was not interrupted in its course in either hemisphere by a superficial 

 bridging convolution. An offshoot of this fissure was prolonged upwards and forwards 

 to the sagittal border of the hemisphere 31 mm. behind the crucial fissure. Sixteen mm. 

 below the splenium the splenial fissure gave origin to a branch which I have named the 

 postero-horizontal fissure (ph) ; it ran horizontally backwards almost as far as the posterior 

 border of the hemisphere. The hippocampal fissure (h) was situated between the 

 hippocampal gyrus and the taenia hippocampi, and curved round the splenium to become 

 continuous with the callosal fissure, which separated the callosal convolution from the 

 corpus callosum. 



These fissures marked out very distinctly an arched convolution, the great limbic 

 lobe of Broca, 1 comparable with the gyrus fornicatus of human anatomy, which may 

 conveniently be divided into callosal and hippocampal convolutions, the latter of which 

 terminated in the uncinate gyrus or lobus hippocampi.- The lobus hippocampi (Ik) was the 

 inferior end of the gyrus fornicatus, and formed the inner part of the posterior lip of the 



1 Strictly speaking, Broca's term " le grand lobe limbique " includes also tlie olfactory lobe, i.e., the olfactory bulb, 

 peduncle, tuber, and roots. 



2 Lobus pyriformis or natiform protuberance of some authors. 



