214 DISSECTION OF THE DOG 



immediately dorsal to it by tearing rather than cutting. This is necessary 

 because the lateral ventricle, a cavity roofed over by the corpus callosum, 

 projects above the level of the medial part of the body. There is, 

 therefore, danger of opening the ventricle if the sUcing process is continued. 



When sufficient of one hemisphere has been removed the other should be 

 treated in the same way. 



In the process of this dissection some features of the inner structure of 

 the cerebrum will be revealed. The depth of some of the sulci will be 

 demonstrated, and the fact that the convolutions are composed of an 

 outer rind of grey matter enclosing a core of white matter will be dis- 

 closed. As the sections become deeper the white cores of the convolutions 



s. siipTaspk'iiialis 



s. inlercalans 



s. crucialus 



s. calcarina ' 



Corpus caWjsum 



Fornix 



Fissura rhinalis 

 Fig. 67. — Medial surface of the cerebral hemisphere. 



become confluent. Finally a large island of white matter occupies the 

 central part of the section of each hemisphere, and is connected by the 

 corpus callosum with a similar island in the other hemisphere. 

 The study of the corpus callosum is best carried out by an examination 

 of the hemi-sected brain in conjunction with that of the specimen just 

 dissected. 



CoRPTTS CALLOSUM. — The corpus callosum is a broad transverse band 

 mainly concerned in connecting the two hemispheres with each other. It will 

 be noted that it is not co-extensive with the hemisphere, but that it coincides 

 roughly with the middle two-fourths of the length of that structure. 



The dorsal surface of the corpus callosum is flat or has a slight convexity. 

 Numerous transverse lines (striae transversae) denote that the body is mainly 

 composed of commissural fibres. In addition, faint longitudinal markings, 

 equivalent to the striae longitudinales of the human brain, may be detected. 



