CONVOLUTIONS AND FISSURES OF SURFACE OF CEREBRUM. 51 





The most important parts of the median hemisphere-wall 

 have been described in the preceding lecture, while we were 

 studying its development. I will only remind you that we then 

 learned that the margin of the hemisphere thickened into the 

 fornix, followed the growing hemisphere in a curve ; that for- 

 ward, where the corpus callosum passes through, that portion 

 of the inner wall which lies between the latter and the fornix,, 

 remains as the septum pellucidum. 



Taught thus by the history of its development, you will 



r 



Of forni*. 



FIG. 31. 



Sagittal section through the middle of an adult brain. The posterior portion of the 

 thalamus, the pedunculus cerebri, etc., have been removed in order to show the inner 

 surface of the temporal lobe. 



understand the sections made through the adult brain. In the 

 specimen from which Fig. 31 is taken, as well as in the embry- 

 onal brain (Fig. 30), all parts lying caudad of the middle of the 

 thalamus are cut off, because they cover the under side of the 

 temporal lobe and prevent us from following up the course of 

 the fornix. 



Now, on the longitudinal section, you see in the centre the 

 inter-brain, or, rather, the thalamus, which has developed from 

 its lateral wall. Along the boundary between it and the cere- 

 brum lies the curved margin of the hemisphere, thickened to a 



