vi] Distribution of the Ti/pes of Cortex lf><t 



limited again by the first temporal sulcus. I must further point out that in this position 

 the area is subject to slight variations, one of which is an extension on to the second 

 temporal gyrus, but on the whole these variations may be regarded as due to changes in 

 form of the hinder extremity of the Sylvian fissure, which in turn are dependent upon 

 variations in the development and representation of the gyri of Heschl. 



Lastly, I think that some of this cortex spreads on to the insula and covers parts of 

 the gyrus longus and gyrus posterior secundus (vide Chapter XL). 



Type III. Again referring to diagram 15 and also to Plate I, it may be seen that 

 in its upper part this area of cortex is contiguous with the field which I shall describe 

 later under the designation " parietal," and the dividing line between the two areas cor- 

 responds approximately but not absolutely with the disposition of the horizontal and occipital 

 rami of the intraparietal fissure 1 . The relation to the ramus occipitalis appears to be more 

 definite than that to the ramus horizontalis, for while temporal characters usually reach up 

 as far as the ramus occipitalis (so covering the angular gyrus), they exhibit an inclination 

 to stop some distance short of the ramus horizontalis : at the same time I must mention 

 that, all along the line, the change in type from temporal to parietal cortex takes place 

 gradually, the only points to be relied on in deciding the transition are the appearance of 

 fibres and cells of greater size than those usually present in the common temporal cortex, 

 and it is really impossible to lay down a sharp line of demarcation. 



The anterior boundary is also an unsatisfactory one, but it to some extent follows the 

 sulcus postcentralis inferior and along this line the temporal gradually passes into the post- 

 central arrangement. 



Posteriorly, I regard the lower division of the ramus occipitalis transversus as a constant 

 boundary, but below this the outskirt of the area is related to no definite fissure and one 

 can only say that it merges with the visuo-psychic cortex, and the point where this junction 

 takes place is roughly indicated by Ecker's suggested anterior limit of the occipital lobe, 

 viz., an imaginary line drawn from the outer extremity of the parieto-occipital fissure to 

 the point on the lower surface of the hemisphere where it is indented by the upper angle 

 of the petrous portion of the temporal bone. The occipital cortex differs so markedly from 

 the temporal that this boundary is readily defined. Coming lastly to the distribution of 

 this area on the temporal lobe proper, it is found that it covers almost the whole of the 

 second and third temporal, and much of the fourth temporal or fusiform gyrus, then spreading 

 on to the inferior and mesial surface it does not cease until the collateral fissure is reached, 

 but as the diagrams show this fissure is not a good boundary. The same type of cortex 

 encircles the tip of the temporal lobe, but behind this a portion of the uncinate gyrus is 

 reserved for the hippocampal type, and the hinder parts of the lingual and fusiform gyri 

 are occupied by visual cortex. 



1 When speaking of tbe intraparietal fissure I shall always adhere to the subdivisions described by Professor 

 Cunningham ; these are the sulcus postcentralis inferior, with the disrupted sulcus postcentralis superior, the ramus 

 horizontalis (commonly joined to the sulcus postcentralis inferior and also known as the sulcus interparietalis of 

 Ecker), the ramus occipitalis (sulcus longitudinalis occipitalis superior of Ecker) and its posterior vertically placed 

 offshoot called by Ecker the ramus occipitalis transversus. 



