156 THE CEREBRAL HEMISPHERES. 



lateral ventricle. The lobe is pierced by the great commissure of the hemispheres (the corpus 

 callosum) and also by the anterior commissure. It is connected by annectent gyri with the 

 lingual gyrus of the temporal lobe (see p. 153), with the cuneus of the occipital lobe (by a 



Fig. 109. DIAGRAM OF THE LIMBIC LOBE. 



gyrus hidden within the internal parieto-occipital fissure), with the quadrate lobule, with the 

 orbital part of the frontal lobe, with the anterior part of the temporal lobe, and with the post- 

 central lobule of the insula. 



Each end of this crescentic lobe is connected with one of the roots of the olfactory tract, 

 viz., the commencement of the gyrus fornicatus with the mesial root and the termination of 

 the hippocampal gyrus with the lateral root. 



CONVOLUTIONS AND FISSURES IN THE LIMBIC LOBE (fig. 102). Gyrns forni- 

 catus, gyrus cinguli, callosal gyrus. This is an extensive convolution which 

 lies between the marginal gyrus of the frontal lobe and the quadrate lobule of the 

 parietal lobe above and the corpus callosum below. The convolution sweeps round 

 the corpus callosum, beginning below its rostrum, where it abuts on the subcallosal 

 gyrus, and ending a little below the level of the splenium by becoming continuous 

 with the posterior end of the hippocampal gyrus. Where it passes into that gyrus 

 it is much narrowed (isthmus). 1 It is separated from the corpus callosum by a fissure 

 which is termed the callosal sulcus. 



The hippocampal gyrus (subiculwn cornu ammonis), also known, together 

 with the infracalcarine, as the uncinate gyrus, is continued from the isthmus of 

 the callosal convolution, and passes forwards above the anterior part of the collateral 

 fissure towards the apex of the temporal lobe (figs. 102, 103). It ends before 

 reaching this, however, becoming considerably thickened, and forming a recurved 

 projection which looks backwards and inwards, and is known as the uncus. The 

 hippocampal gyrus is covered superficially by a well-marked reticular layer of white 

 fibres (s'ubstantia reticularis alba, Arnold (fig. 103, s.r.a.) ). 



The dentate gyrus (fascia dentata Tarini(fi.g. 102, fig. 110, f.d.) ) lies above the 

 hippocampal gyrus, from which it is separated by the hippocampal or denlatefissure (f.ti). 



1 By some authors the term gyrus fornicatus is made to include the hippocampal gyms. 



