CORPUS CALLOSUM. 479 



The olfactory bulbs, the apparent origin of the first pair of 

 cranial nerves, arise from the anterior perforated spaces. They 

 consist of a layer of white, surrounding an inner tube of grey 

 matter, the interior being hollow, and communicating with the 

 lateral ventricles. 



CORPUS CALLOSUM. 



On removing the upper part of the hemispheres, by a section 

 midway between the corpus callosum and the superior surface of 

 the brain, a central mass of white matter, surrounded by a 

 convoluted border of grey, is exposed. The white portion, 

 known as the centrum ovale minus, is studded with numerous 

 red spots, puncta vasculosa, caused by the escape of blood from 

 the vessels which have been divided. A second section, made 

 immediately above the' corpus callosum. exposes the greatest 

 amount of white matter, centrum ovale ma jus, above which, on 

 the inner surface of the hemisphere, is the yyrus fomicatus, a 

 convolution which follows the curve of the corpus callosum. The 

 space between this convolution and the corpus is known as the 

 wiifride of the corpus callosum. 



The corpus callosum, or great commissure (trabs cerebri), is 

 the white, quadrilateral, and arched body which unites the hemi- 

 spheres. Its lateral borders are hidden by the gyri fornicati and 

 substance of the hemispheres, in which they become lost ; while 

 the middle of its superior surface, seen at the bottom of the 

 longitudinal fissure, is free, and covered with pia mater. Along 

 its middle line, between two delicate cords of white matter (strice 

 longitudinales} runs a line or seam, the raphe, on either side of 

 which may be seen the transverse markings, which indicate the 

 direction of the fibres of which the corpus callosum is composed. 

 Its inferior surface is connected posteriorly with the fornix, the 

 remainder being divided by the septum lucidum into two parts, 

 which form the roofs of the lateral ventricles. Its anterior 

 extremity is reflected downwards, the bend being the knee or 

 genu, and the tapering reflection the rostrum or beak. From 

 the sides of the rostrum a delicate grey membrane, the lamina 

 cinerea, extends to the tuber cinereum, and from the point 

 divergent white bands, the crura of the corpus, extend to the 

 anterior perforated spaces. The posterior extremity of the 

 corpus callosum is thick, and forms a free rounded border, which 

 is in connection with the fornix. 



