49 o TEXT-BOOK OF PHYSIOLOGY. 



parietal fissure to its termination. At this point it makes a sharp 

 bend and runs forward into the temporal lobe just beneath the 

 first temporal fissure. In the neighborhood of the bend it is 

 generally known as the angular convolution or gyms. 

 The Temporo-sphenoidal Lobe. The temporo-sphenoidal 

 lobe presents on its external surface three well-marked convolutions : 

 viz., the superior, the middle, and the inferior temporal, separated by 

 the first and second temporal fissures. These three convolutions are 

 in a general way parallel with each other, and pursue a direction 

 from before backward and upward. Anteriorly, they are fused to- 

 gether, but posteriorly their connections are somewhat different. 

 The superior temporal is continuous behind and above with the 

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

 convolution or gyre. The middle temporal blends with the preceding 

 and with the middle occipital. The inferior temporal is continuous 

 with the inferior 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 inferior occipital. 



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

 by the frontal, the parietal, the occipital, and the temporal lobes, pre- 

 sents several convolutions of much physiologic interest, viz. : 



1. The gyrus fornicatus, situated between the calloso-marginal 



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 gyrus hippocampus, formed by the union of the posterior 



extremity of the gyrus fornicatus and the median occipito- tem- 

 poral convolution (the lingual lobule), 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 gyrus fornicatus, 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 infracallosal gyrus. 



