THE BRAIN. 191 



posterior extremity (the splenium), where it turns upward 

 to the margin of the hemisphere. 



In front of the fissure of Rolando there is an offset 

 from the callosomarginal sulcus which serves to bound 

 anteriorly the paracentral convolution. Also, the direction 

 of the main part of the sulcus is continued posteriorly 

 nearly to the parieto-occipital fissure under the name of the 

 subparietal sulcus. This sulcus is often not distinctly 

 marked. 



The curved portion of cerebral matter external to the 

 callosomarginal sulcus belongs to the frontal lobe and is 

 called the marginal convolution. As above stated, the 

 portion of the marginal lobe which connects the ascending 

 frontal and parietal convolutions is called the paracentral 

 convolution. 



The square-shaped mass between the upturned extremity 

 of the callosomarginal sulcus and the parieto-occipital 

 fissure is the quadrate lobe, or convolution. It is the 

 internal portion of the parietal lobe and is limited inferiorly 

 by the subparietal sulcus. 



Between the posterior portion of the parieto-occipital 

 and the calcarine fissures is the triangular or wedge-shaped 

 convolution the cuneus which is the internal part of the 

 occipital lobe. The marginal, quadrate, and cuneate con- 

 volutions form the outer arch of the internal surface of the 

 hemisphere. 



Internal to this outer arch of convolutions is a second 

 arch, which starts beneath the anterior extremity of the 

 corpus callosum, curves backward over that structure, being 

 separated from it by the callosal sulcus, then turns around 

 the hinder extremity of the corpus callosum, and under the 

 name of the uncinate convolution extends forward to the 

 end of the temporal lobe. 



