586 TEXT-BOOK OF PHYSIOLOGY 



post-central convolution. Passing backward, it winds around the 

 superior extremity of the fissure of Sylvius, in which situation it is known 

 as the supra-marginal convolution. Beyond this point it divides into 

 two portions, one of which runs forward into the temporal lobe above 

 the super- temporal fissure, while the other runs downward and back- 

 ward, following the intra-parietal fissure to its termination. At this 

 point it makes a sharp bend and runs forward into the temporal lobe 

 just beneath the super-temporal fissure. In the neighborhood of the 

 bend it is generally known as the angular convolution or gyrus. 

 The Temporo-sphenoidal Lobe. Thetemporo-sphenoidal lobe presents 

 on its external surface three well-marked convolutions: viz., the super-, the 

 medi-, and the sub-temporal, separated by the super- and medi-temporal 

 fissures. These three convolutions are in a general way parallel with each 

 other, and pursue a direction from before backward and upward. Ante- 

 riorly, they are fused together, but posteriorly their connections are some- 

 what different. The super-temporal is continuous behind and above with 

 the supra-marginal convolution, and behind and below with the angular 

 convolution or gyrus. The medi-temporal blends with the preceding and 

 with the middle occipital. The sub-temporal is continuous with the in- 

 ferior occipital. 



The Occipital Lobe. The occipital lobe is triangular in shape and 

 forms the posterior apex of the hemisphere. Its base on the external 

 surface is formed by an imaginary line drawn from the parieto-occipital 

 fissure to the pre-occipital notch on the inferior and lateral border. The 

 external surface presents three convolutions the superior, middle, and in- 

 ferior occipital. 



The inner or mesial surface of the hemisphere, formed in part by the 

 frontal, the parietal, the occipital, and the temporal lobes, presents several 

 convolutions of much physiologic interest, viz. : 



1. The callosal convolution, or gyrus, situated between the super-call osal 



fissure and the corpus callosum. From its origin anteriorly at the base 

 of the brain this convolution passes backward, gradually increasing in 

 width as it approaches the posterior extremity of the corpus callosum. 

 At this point it again narrows and descends between the calcarine and 

 hippocampal fissures to blend with the hippocampal convolution. 



2. The hippocampal gyrus, formed by the union of the posterior extremity 



of the callosal convolution and the sub-calcarine gyrus or the gyrus 

 lingualis, is situated just below the dentate or hippocampal fissure. 

 Anteriorly it becomes enlarged, and just behind the apex of the 

 temporal lobe turns backward and inward to form a hook-shaped 

 eminence, the uncinate gyrus or uncus. 



The limbic lobe is the name given to an area of the brain which 

 includes, among other structures, the callosal convolution, the gyrus 

 hippocampus, and the uncus. As forming a part of this general 

 lobe may be mentioned the dentate fascia, the striae and peduncle of 

 the corpus callosum, the septum lucidum, the fornix, and the in- 

 fra-callosal gyrus. 



3 . The sub-collateral convolution or gyrus or the gyrus fusiformis is bounded 



by the collateral fissure above, and its inferior border extends from 

 the occipital lobe to the anterior pole of the temporal lobe. 



