THE TEMPORAL CONVOLUTIONS. 755 



of it is the parieto-occipital, and below the calcarine fissure. Small 

 irregular .sulci divide it into secondary gyri. 



The uncinat>: or fifth temporal conwlvtw* (u) extends from the Uncinate 

 pustt-rior extremity of the hemisphere behind to the Sylvian fissure aB 

 in front, being bounded by the calcarine and hippocampal fissures 

 ibove, and by the collateral fissure belo\v. It is somewhat 

 narrowed in the middle, where the callosal convolution joins it, 

 and enlarged in front and behind. At its fore part is a small 

 piece (itncus) bent backwards over the lower end of the dentate 

 tKsure, and from this feature the convolution derives it name. The 

 posterior part of the convolution, that which is limited above by the lingual 

 calcarine fissure, is often described as the lingual convolution. lutions 



The fourth temporal, or occipito-temporal, convolution (EOT) lies Fourth 

 between the collateral fissure and the third temporal sulcus (it). Involution. 

 This is frequently not distinct from the third temporal convolution, 

 which forms the outer margin of the temporal lobe in the greater 

 part of its extent. 



At the bottom of the dentate fissure, the grey cortex of the 

 hemisphere ends in a projecting notched margin, which is named Dentate 

 the fascia duitata or the dentate convolution (FD). This will be better gyms, 

 seen subsequently. 



.i.ctuTK of the convolutions. Each convolution is continuous Form and 

 with the general mass of the hemisphere on the one side and is JonSiu 

 tree on the other, where it presents a summit and lateral surfaces, tions J 

 which are covered by pia mater. A cross section will show it to 

 consist of a layer of cortical grey substance on the surface, which grey. 

 is continued at the bottom of the sulci from one eminence to another, 

 nul of a white medullary part in the centre, which appears as a and white 

 process of the large medullary mass forming the greater part of the jSJuf ^ 

 substance of the hemisphere. On examining closely the section of a 

 convolution in a fresh specimen, the cortex may generally be seen to Structure of 

 consist of three grey, and of intermediate white, layers arranged c 

 alternately, covered externally by a thin white stratum, which is 

 most marked over the fore part of the uncinate convolution. 



If a portion of the cuneate lobule be taken it will be found that 

 the fourth layer of the cerebral cortex is particularly distinct as a 

 white line running in the grey matter. 



INTERIOR OF THE CEREBRUM. 



Each cerebral hemisphere consists of white and grey substance, Outline of 

 the white forming the larger portion of the mass (medullary centre ce 

 of the hemisphere), while the grey matter is chiefly disposed in a 

 superficial layer (cortex) which covers the medullary centre, except medullary 

 over the region on the inner side whence the corpus callosum issues ; 



centre ; 



but at the lower part of the hemisphere there are other collections cortical 



and cent 

 grey masses; 



of grey matter more or less surrounded by the medullary substance. ar 



In each hemisphere is an elongated cavity, named the lateral 

 ventricle, which communicates with another median space the ventricles. 

 third ventricle, placed close to the base of the brain. 



3c 2 



