350 ANATOMY OF THE RABBIT 



more expanded part of the cerebral cortex. The slight 

 angle formed at the junction of the anterior and posterior 

 rhinal fissures is the point of origin of a faint depression 

 extending upward on the lateral surface of the cerebral 

 hemisphere. This represents a rudiment of the lateral 

 cerebral (Sylvian) fissure, which is a conspicuous feature 

 in the brain of man and other mammals with convoluted 

 hemispheres. 



Fig. 115. Dissection to show the radia- 

 tion of the corpus callosum from a dorsal 

 viewpoint. The longitudinal white line 

 close to the median plane is the position of 

 a delicate band of hippocampal fibres, the 

 medial longitudinal stria. 



(d) The corpus callosum is a broad, white commissural band 

 passing transversely between the hemispheres (Fig. 115) to 

 connect the cortex of each with that of the other and thus 

 providing for the co-ordination of their action. Its median 

 portion lies at the bottom of the longitudinal cerebral fissure 

 and may be exposed dorsally by pressing apart the medial 

 margins of the hemispheres so as to open up the fissure. 

 The foregoing parts belong to the telencephalon, those which 

 follow belong to the diencephalon (p. 86). 



^Though the term is sometimes loosely used, a commissure may be defined as 

 a structure connecting corresponding parts on opposite sides. It contrasts with 

 a decussation, which is a system of nerve-fibres crossing the median plane to 

 connect different parts on the two sides. 



