THE FOKM-EELATIONS OF THE HUMAN BRAIN. 



199 



name of gyrus hippocampi is given to the part lying posterior and ventral. 

 Posteriorly, as is well seen in the figure, a small, longish convolution of the 

 occipital lobe joins the gyrus hippocampi; it is called the gyrus lingualis. 



As has previoiisly been shown, the fornix forms the edge of the hemi- 

 sphere. The first portion of the wall of the brain succeeding this is the 

 above-mentioned gyrus hippocampi, which is, therefore, adjacent to the 

 fornix. Externally to it lies the cavity of the ventricle: the inferior horn. 



The ventricle is separated at this place from the cranial cavity by a 

 thin, vascular membrane only, — the continuation of the plexus chorioideus, 

 — which is attached to the fornix throughout its entire extent. 



The gyrus hippocampi is covered by cortical matter, but the cortex 

 ceases on the side toward the inferior horn; and, close to the ventricle, the 

 white medullary substance, no longer covered by gray matter as on the entire 



I'ig. 134a. 



Fig. 1340. 



Fig. 134c. 



Fig. 134a. Fig. 1346. Fig. 134e. TJnterhorn, Inferior horn. 



outer surface of the brain, lies exposed. This medullary substance — a long, 

 white stripe, which is directly continuous with the fornix above — is called 

 the fimbria (Pig. 133). 



The marginal convolution is pushed by a fissure of its outer surface — 

 the fissura hippocampi — into the cavity of the inferior horn. The elevation 

 thus produced along the entire fioor of the inferior horn has borne for cent- 

 uries the name of cornu Ammonis, or pes hippocampi major. 



Owing to the fact that the cortex of the gyrus hippocampi is also infolded by 

 that fissure before the cortex entirely ceases and leaves the medullary substance ex- 

 posed, there is presented a peculiar, somewhat complicated section, if the gyrus is 

 cut transversely. On other parts of the brain the cortex covers the surface con- 

 tinuously, as is shown in Fig. 134a; it ceases, however, close to the ventricle at 

 the marginal infolding, and leaves exposed a white, somewhat curved border, the 



