THE EXTERNAL CONFIGURATION OF THE CEREBRAL HEMISPHERES 239 



where the calcarine is joined by the parieto-occipital fissure. The other portion, 

 sometimes called the ''posterior calcarine sulcus," arches downward and back- 

 ward from this junction toward the occipital pole, and occasionally cuts across 

 the border of the hemisphere to its dorsolateral surface. The parieto-occipital 

 fissure, which is really a deep fossa with much buried cortex at its depth, appears 

 to be the direct continuation of the rostral part of the calcarine fissure. It cuts 

 through the dorsal border of the hemisphere somewhat nearer to the occipital 

 pole than to the central sulcus. These fissures form a Y-shaped figure whose 

 stem is the calcarine fissure and whose two limbs are the parieto-occipital fissure 

 and the "posterior calcarine sulcus." If the fissures are opened up the stem is 

 seen to be marked off from the two limbs by buried annectant gyri. 



The cuneus is a triangular convolution with apex directed rostrally, which 

 lies between the diverging parieto-occipital and calcarine fissures. The rest of 

 the medial surface of the occipital lobe belongs to the lingual gyrus, which lies 

 between the calcarine and collateral fissures. 



The remaining sulci and gyri on the median and basal surfaces may now be 

 briefly described. 



The sulcus of the corpus callosum (sulcus corporis callosi) begins ventrally to 

 the rostrum of the corpus callosum, encircles that great commissure on its con- 

 vex aspect, and finally bends around the splenium to become continuous with 

 the Mppocampal fissure (Fig. 171). The latter is a shallow groove, which runs 

 from the region of the splenium of the corpus callosum toward the temporal 

 pole near the dorsomedial border of the temporal lobe. It terminates in the 

 bend between the hippocampal gyrus and the uncus. 



The sulcus cinguli (callosomarginal fissure) begins some distance ventral 

 to the rostrum of the corpus callosum and follows the arched course of the 

 sulcus of the corpus callosum, from which it is separated by the gyrus cinguli. 

 It terminates by dividing into two branches. One of these, the sub parietal 

 sulcus, continues in the direction of the sulcus cinguli and ends a short distance 

 behind the splenium. The other, known as the marginal ramus, turns off at a 

 right angle and is directed toward the dorsal margin of the hemisphere. A side 

 branch, directed florsally, is usually given off from the main sulcus some dis- 

 tance rostral to its bifurcation, and is known as the paracentral sulcus. 



The collateral fissure begins near the occipital pole and runs rostrally, sepa- 

 rated from the calcarine and hippocampal fissures by the lingual and hippo- 

 campal gyri. It is sometimes continuous with the rhinal fissure. The latter 

 separates the terminal part of the hippocampal gyrus, which belongs to the archi- 



