22 Precentral or Motor Area [CHAP. 



In regard to the superior germ, Professors Sherrington and Griinbaum have already 

 insisted upon its constancy as a divisional landmark between the leg and arm areas ; my 

 histological studies also show that there is a curious structural transition at this level ; it is 

 therefore important that we should examine the morphology of the flexure closely. 



Now, it is a fact known to anatomists, and one which I have verified by the examination 

 of several hundreds of brains and casts which I have placed in the museum at Rainhill Asylum, 

 that when the lips of the fissure of Rolando are drawn apart, a deep annectant gyrus, giving 

 rise to some shallowing of the fissure, is displayed in the vicinity of the upper genu ; inspected 

 more minutely, it is found that this formation may be correctly described as consisting of inter- 

 digitating gyri, or buttresses, springing from the apposed walls of the fissure, and, in by far 

 the majority of brains, the most constant, the most prominent, and in my opinion the most 

 important element in the formation, is the large bulging buttress on the precentral wall, for 

 the accommodation of which the post-central wall suffers indentation. Occasionally, the frontal 

 buttress is reduplicated by a vertical fissure, but this does not diminish its relative prominence, 

 which is always obviously greater than that of the one or more parietal buttresses with which 

 it interlocks. Studied in its relation to other parts, we notice that it is invariably placed on 

 a level with, or, more correctly speaking, slightly above the superior genu, and, furthermore, 

 there is not the slightest doubt that, at any rate in the human brain, this upper, backward 

 curve in the fissure of Rolando is entirely attributable to the presence of the great precentral 

 buttress, and, when that genu occupies an abnormally high or low position, the buttress is 

 correspondingly changed. Another fairly constant guide to the localisation of the buttress is 

 the hinder extremity of the superior frontal sulcus, which is commonly placed on the same 

 horizontal level and serves as a pointer. 



Proving the morphological importance of this buttress, I may further mention that, not 

 uncommonly, it is so strongly developed as to almost reach the surface, and occasionally it 

 rises completely and divides the fissure of Rolando into two distinct and separate parts. The 

 latter condition is regarded by Cunningham as one of " extreme rarity," but this expression 

 does not tally with my observations, for in a routine examination of 1400 brains I have noticed 

 the formation in 13 instances, approximately 1 / J - 



Associated with the extraordinary development of the annectant gyrus. an unusual dis- 

 position of adjacent sulci was commonly noticed, but these need not be detailed. 



In considering the significance of an interrupted fissure of Rolando it is interesting to learn 

 what happens in course of development, and to hear that Professor Cunningham, after examining 

 numerous foetal brains, has arrived at the conclusion that the fissure is originally laid down 

 in two separate pieces, and that the joining of these two elements is indicated in the mature 

 brain by the annectant gyrus under consideration. Now if this view of the development of the 

 Rolandic fissure be correct, it obviously follows that the presence of the annectant on the surface 

 is nothing more than an expression of the remains of a foetal condition, and this sequence gains 

 in likelihood when it is mentioned that no less than 4 out of the 13 brains exhibiting the 

 anomaly which I have collected were obtained from cases of idiocy and cases in which the 

 gyral disposition followed a simple plan. 



1 Eight of these cases were males and five females, in seven instances the arrangement occurred in the right 

 hemisphere, in five it affected the left, and in one case, a male, it was bilateral. 



