688 THE XERVOUS SYSTEM 



and a superior, which is situated within the Sylvian fissure and can be displayed 

 by pulling up the operculum. 



The boundaries of the temporal lobe have been already indicated in the description of the 

 other lobes, but may be recapitulated as follows. It is bounded behiiid by the lower part of the 

 line drawn from the external jiarieto-uoeipital fissure to the prieocciitital notch. Above, it i.s 

 limited hv tlie huriznntal part of the posterior limb of-the Sylvian fissure and by a line continuing 

 the horizitntal direction backwards to meet the posterior boundary. Its tentorial surface may be 

 marked off from the occipital lobe by a line drawn from the praeoccipital notch to the isthmus of 

 the gyrus fornicatus. 



Three fissures traverse the temporal lobe in a direction parallel to its long axis. 

 The first of these, the superior temporal or parallel fissure, is one of the most con- 

 stant of the incomplete fissures of the cerebrum. The other two, termed middle 

 and inferior temporal, seldom appear as well-marked sulci, being as a rule broken 

 up by fissures and gyri crossing at right angles to their direction. 



The collateral fissure on the tentorial surface is approximately parallel to the three temporal 

 sulci ; it marks off the temporal from the falciform lobe. 



The parallel fissure commences a short distance behind the apex of the lobe, 

 and takes a course parallel to the posterior limb of the fissure of Sylvius. Its 

 U])turned extremity ends in the parietal lobe, where it is embraced by the angular 

 gyrus. 



The middle temporal fissure runs in the same general direction as the parallel 

 fissure but is placed at a hjwer level. It may communicate behind with the sulcus 

 occipitalis anterior. 



The inferior temporal fissure is placed on the under surface near the lateral 

 margin of the hemisphere. It is in a line with the inferior occipital fissure. 



Three convolutions are j^resent on the outer surface, running in an antero- 

 posterior direction. They are termed the superior, middle, and inferior temporal 

 convolutions. They liecome confluent witli one another at the apex of the lobe. 



The superior temporal or inframarginal convolution lies between the Sylvian 

 and parallel fissures. It is continuous alujve witli the supramarginal and angular 



The middle temporal convolution, placed between the parallel and the middle 

 temporal fissures, is continuous behind with the angular gyrus and the post-parietal 

 convolution. It is usually joined to the inferior occipital by the fourth annectant 

 gyrus. 



The inferior temporal convolution is situated on the lateral margin of the 

 hemisphere. It may Vje coni^'cted to the inferior occipital convolution by a fifth 

 annectant gyrus. 



The superior surface of the temporal lol)e is in contact with the operculum. It 

 is crossed by two or three (sometimes four) transverse temporal convolutions. 

 (Heschl. ) 



Dissection. — The .student should now raise the operculum and at the same time draw the 

 temporal lobe downwards in order to bring the island of Reil into view. The large branches of 

 the middle cerebral artery which lie among the convolutions of the island should be removed, 

 together with the adherent pia mater. 



The CENTRAL LOBE or ISLAND OF REIL corresponds to the floor of the 

 embryonic fossa Sylvii, and is placed external to the claustrum. Its form is tri- 

 angular; the base of the triangle is placed upwards and inwards, the apex forms a 

 prominence, the limen insube, which separates the vallecula Sylvii from the fissure 

 of the same name. It is hidden by tin; o]»er('ula and is sin-rounded, except at the 

 limen, by a curved furrow, the sulcus circularis Reilii (Schwalbe). From five 

 to seven convolutions, the gyri operti, radiate from the limen insula^. The island 

 is divided into a larger anterior j)art (pars frontalis), and a sn)aller posterior part 

 (pars parieto-falciformis ) by a constant fissure, the sulcus centralis insulae 

 (Hefltler and Kberstaller;, which has the same direction, and is in the same plane, 

 as the fissure of Rolando, 



