BASE OF BHAIN, OPTIC NERVE, AND COEPOEA QUADEIGEMINA. 393 



widely opened and covered by the tapetum, leads at its dorsal end into the posterior 

 horn; at its ventral end, however, — where mesially the gyrus hippocampi is still 

 found to be cut, — it leads into the inferior horn of the temporal lobe. Dorsal to 

 the cornu Ammonis is found the large mass of fibers of the corpus callosum, which 

 pass from the terminals in the occipital lobe to the forceps major {Balkenwulst) and 

 are here cut just before they enter the spleniura. 



We now meet with the radiatio oceipito-thalamica in greater width than 

 hitherto outside of, and lateral to, the tapetum. It here lies under the convolu- 

 tions of the temporal lobe, and this position explains why lesions in the gyrus 

 marginalis or angularis frequently lead to hemianopsia. If the lesions are not 

 altogether too superficial, they always of necessity involve the optic radiation. 



Fore. Corp. callos. 



Cunens 



Rad. occipito-thulaiii. 



Fiss. eiilcarinn 



Veutricnlua 



G3'nis lingualia 

 Fasc. long. inf. 



Gyrus fusiformia 



Fiss. iiiterparieb. 

 Ijolt. pariet. inf. 



Fiss. temp. sap. 



Fig. 189. 



The fasciculus longitudinalis inferior also (the tract from the occipital lobe to 

 the temporal lobe), the transverse section of which, as in the previous sections, you 

 again find external to the optic radiation, is here wider than previously, because we 

 now approach the territory where it originates. The peculiar oblique form of the 

 under side of the section is explained from the fact that the hemispheres of the 

 cerebellum, separated by the tentorium alone, here lie against the cerebrum. 



You finally see a section (Fig. 189) which 1 have made through the occipital 

 lobe very near to the posterior pole of the brain. The posterior horn of the ventricle, 

 which is still just visible as a, small fissure, may again serve as a point of orientation 

 in obtaining the relation of the fibre-systems to one another and as a whole. 



From the neighborhood of the fissura calcarina, which here cuts in deeply, 

 arises the optic radiation, which we have now traced from its origin to its termi- 



