CONVOLUTIONS AND FISSURES OF SURFACE OF CEREBRUM. 53 



central convolution. That part lying in front of and above this 

 fissure is considered as belonging to the superior frontal convo- 

 lution. The convolution between it and the corpus callosum is 

 called the gyrus fornicatus. A glance at a specimen, or at our 

 cut, shows that the gyrus fornicatus becomes widened posteriorly, 

 and passes up over the crest of the hemisphere to become con- 

 tinuous with the superior parietal lobe. This widened portion 

 is called the pmecuneus. Directly in front of the praecuneus 

 lies a region of the cortex which, exteriorly, is continuous with 

 both central convolutions and connects them. It is called the 

 paracentral lobule. Posteriorly, the prrecuneus is bounded by a 

 deep fissure, which usually passes over somewhat to the exterior 

 surface of the hemisphere. It is called the parieto-occipital 

 fissure. This parieto-occipital fissure sometimes passes beyond 

 the inner surface of the brain, and runs out over the outer 

 surface as a deep perpendicular fissure. This is especially apt 

 to occur in the brains of idiots. 



The fissura calcarina joins the parieto-occipital sulcus at 

 an acute angle. This fissure lies exactly in the wall of the 

 posterior horn of the lateral ventricle, which has been mentioned 

 before. The brain-wall, displaced inward by it, can be seen as 

 an elongated swelling in the posterior horn. This swelling is 

 known as the calcar avis or pes hippocampi minor. The tri- 

 angular portion of cortex inclosed between the fissures last 

 described is known as the cuneus. Examine the point of this 

 region and, superficially or deeply, you will find a little convo- 

 lution connecting it with the gyrus fornicatus, which passes by 

 in front of the wedge-shaped cuneus. Notice this comparatively 

 narrow part of the gyrus fornicatus. You see that it passes on 

 as a rapidly-broadening convolution to the apex of the temporal 

 lobe, where it ends in a hook-shaped process, the uncus or gyrus 

 . uncinatus. This part of the gyrus fornicatus lying in the tem- 

 poral lobe is called the gyrus hippocampi. Posteriorly (as you 

 see in the cut), a small, longish convolution of the occipital lobe 

 joins the gyrus hippocampi. It is called the lobus lingualis. 



