THE COMMISSUEES. 



241 



Besides these fibers, which connect parts of the same hemisphere with 

 each other, there are also fibers that connect one half of the cerebrum with 

 the other. Almost all of these fibers run in the corpus callosum and in the 

 anterior commissure, thus passing transversely through both hemispheres 

 from one to the other. 



Inasmuch as I presuppose that the macroscopic relations of the corpus 

 callosum are known to you — at least its general form, where it is distinct 

 from the other brain-mass — little remains to be said by way of explanation 

 of the accompanying illustration (Fig. 157). 



It must be borne in mind that Just as the fibers of the corpus callosum 

 are seen passing transversely from side to side in this section (which is made 

 about through the chiasma), so they are to be seen in the whole region of the 

 brain over the lateral ventricles. 



Fig. 157. — Frontal section through the forebrain. Diagram of the course 

 of the corpus callosum and the commissura anterior. 



From the frontal lobe, also, the corpus callosum receives on each side 

 a large afferent bundle that grows to it anteriorly over the roof of the lateral 

 ventricle, on its lateral side. The fibers of the corpus callosum from the 

 occipital lobe closely surround the posterior horn like a cap. Their radia- 

 tion is known as the forceps major. The portion of the corpus callosum 

 passing into the temporal lobe on the lateral side of the inferior horn is 

 called the forceps minor. The inner side of the posterior horn and that of 

 the inferior horn are covered by a layer of white, meduUated fibers, the 

 tapetum. (Compare the sections through the fibers of the corpus callosum 

 which are shown in Figs. 169 to 174 and 185 to 188.) 



The simple methods of sectioning formerly employed made this entire layer 

 originate like the fibers of the corpus callosum, — made it appear, in a measure, as the 



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