752 



DISSECTIOX OF THE BRAIN. 



Temporal 

 sulci : 



lirst or 

 parallel, 



second, and 

 third. 



Convolu- 

 tions. 



Convolu- 

 tions, of 

 island of 

 Reil. 



Sulci and 

 convolu- 

 tions of 

 inner and 

 tentorial 

 surfaces. 



How to see 

 them. 



Calloso- 

 marginal 

 sulcus. 



SULCI AND CONVOLUTIONS OF THE OUTER SURFACE OF THE 



TEMPORAL LOBE (fig. 270). There are live convolutions of this 

 lobe ; the first, second and a part of the third, with their inter- 

 vening sulci, are seen on the outer surface and the remainder 011 

 the under aspect of the cerebral hemisphere. 



The ./fart temporal or parallel sulcus (st) is well marked, and runs 

 below and parallel to the posterior branch of the fissure of Sylvius, 

 from near the anterior extremity of the lobe, backwards and 

 upwards, into the inferior parietal lobule. The second temporal 

 sulcus (rut) takes a similar course at a lower level, but it is not so 

 constant as the superior; and the third (fig. 273, it\ which is also 

 very variable, is placed on the under surface of the hemisphere near 

 the margin, separating the third from the fourth convolution. 



The jirsi temporal convolution (inframarginal ; fig. 270, ST) forms 

 the lower boundary of the posterior branch of the Sylvian fissure, 

 and is continuous behind with the supramarginal convolution. 

 The second and third temporal convolutions (MT and IT) are com- 

 monly united in some part of their extent. The posterior end of 

 the second one is joined by the angular and post-parietal gyri. 

 The third forms the lower margin of the lobe and joins the post- 

 parietal and lowest occipital gyri. 



CONVOLUTIONS OF THE CENTRAL LOBE (figs. 271 and 272, c). 

 The surface of the insula is divided by an oblique furrow the 

 central sulcus of the insula, placed opposite the lower end of the 

 furrow of Rolando, into an anterior triangular, and a posterior 

 more elongated portion. The anterior part is again subdivided 

 externally into three small gyri breves, and the posterior part into 

 two gyri longi. 



SULCI AND CONVOLUTIONS OF THE INNER SURFACE OF THE 



HEMISPHERE (fig. 273). The convolutions of the inner aspect of 

 the hemisphere, with which are included those of the lower surface 

 behind the fissure of Sylvius, are generally well defined ; but some 

 being so long as to reach beyond the extent of a single lobe of the 

 outer surface, they are not usually like those described as forming 

 lobes. 



Dissection. The parts to be now described can only be seen 

 satisfactorily on a separate hemisphere, and if the students are 

 working with two brains, one of the hemispheres on that brain in 

 which the cerebellum and other parts have been removed, should be 

 used by separating it from its fellow by a mesial incision. If, 

 however, the student possesses only the one brain, he may show 

 much of the inner surface by cutting off the left hemisphere as low 

 as the corpus callosum and examining the right side and the under 

 surface of the left. 



SULCI. The calloso-marginal sulcus (cm) begins below the rostrum 

 of the corpus callosum, and arches upwards, following the curve of 

 the fore part of that body. It is then directed backwards as far as 

 the posterior extremity of the corpus callosum, where it bends 

 upwards and ends by notching the superior margin of the hemi- 

 sphere (fig. 270, cm). Its fore part is frequently interrupted by 



