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



the corpus callosum, where it formed the genual j>art of the callosal convolution, to reach 

 the basal part of the mesial longitudinal fissure. The suprasplenial fissure (ssp) of 

 Krueg was as a rule elementary, but in the right hemisphere of brain c it was a distinct 

 fissure situated on the mesial surface of the hemisphere parallel to the splenial fissure, 

 and separated from it by a distinct gyrus, which may be called the suprasplenial gyrus. 

 It was continuous behind the splenium with the splenial fissure, whilst it terminated 

 anteriorly in a sulcus, which indented the sagittal gyrus above the crucial fissure. 

 Between the suprasplenial fissure and the free edge of the mesial longitudinal fissure 

 was that aspect of the sagittal gyrus which was directed to the mesial marginal 

 surface of the hemisphere. The postsplenial fissure (psp) of Krueg was situated 

 behind the ascending part of the splenial fissure, and ran backwards and upwards 

 nearly to the posterior border of the hemisphere below the postero-horizontal fissure ; 

 it was separated from the splenial fissure by the splenial convolution (sj)c), which is 

 consequently bounded in front by the splenial and behind by the postsplenial fissure. 



I could not speak with any precision of the Island of Reil, unless the concealed part 

 of the anterior limb of the Sylvian convolution be regarded as representing it ; for the 

 lower end of this limb of the Sylvian convolution passed deeply into the fissure, and 

 was concealed by the anterior limb of the suprasylvian convolution, which for some 

 distance therefore formed the anterior lip of the fissure of Sylvius. 



Interior ofi the Cerebrum. — A vertical transverse section through the right hemisphere, 

 immediately in front of the anterior pillar of the fornix, showed the fibres of the corpus 

 callosum extending outwards to become continuous with the white core of the hemisphere. 

 Immediately below the anterior mesial part of the corpus callosum the right half of the 

 septum lucidum formed a vertical lamina which was relatively thick. Laterally to the 

 septum lucidum was the lateral ventricle, the inner part of which was vertical, but the 

 outer part extended horizontally outwards below the corpus callosum, though it curved a 

 little downwards at its lateral limit. When the ventricle was opened into by slicing 

 away the corpus callosum the nucleus caudatus of the corpus striatum was seen to form 

 a large and well-defined pear-shaped body at the anterior part of the floor ; but the 

 ventricular chamber was not prolonged in front of the caudate nucleus. The greatest 

 transverse diameter of this nucleus was 27 mm., and its antero-posterior diameter was 

 30 mm. 



The optic thalamus was behind and to the inner side of the nucleus caudatus, a 

 shallow groove in which the tsenia semi-circularis could be seen, being placed between 

 them. Its upper surface was covered by the fornix and choroid plexus, on removing 

 which structures this surface was seen to be 25 mm. in transverse and 35 mm. in antero- 

 posterior diameter. 



The fornix was prolonged in a curve backwards, outwards, downwards, and forwards 

 into the descending horn of the ventricle as the tsenia hippocampi, and followed the 



