97 



Smith (9) has shown how constantly such arrangements depend on 

 the tension of neighbouring cortical growth. 



The compression of the sensory area above described leads to 

 the disappearance of the sulcus praeparietalis as a recognisable integer. 

 There can be no doubt however but that it is represented by one of the 

 offshoots from the sulcus post-centralis, which is thus a composite 

 furrow. In the diagrams I have not ventured to mark any definite 

 portion of the superior postcentral sulcus as being really sulcus prae- 

 parietalis. But it will be realised that any portion of the superior post- 

 central which abandons its limiting function and encroaches upon the 

 sensory area is very likely representative of the sulcus praeparietalis 

 of pithecidae. The only way of deciding which part, if any, is prae- 

 parietal and which postcentral in a given case (I use the term post- 

 central throughout as referring to the specific sulcus, since all these 

 furrows in common lie behind the sulcus centralis) is by laborious 

 histological investigation. I firmly believe the naked-eye method of 

 Elliot Smith to be far superior to the microscopic method. But 

 in this country at any rate the necessary conditions are not easily 

 fulfilled. 



It is obvious from the foregoing that the sulcus postcentralis 

 superior is a composite furrow capable of resolution into its constituent 

 parts : 



(1) A sulcus separating the area post-centralis caudalis from the 

 area parietalis superior. 



(2) A sulcus praeparietalis (mihi), separating the area of the same 

 name from the area post-centralis caudalis. 



(3) A sulcus of varying dimensions, the sulcus paracinguli which 

 bounds the arcus cinguli (mihi). 



This last must be considered as a more or less accidental inclusion, 

 but it is so frequent an occurrence as to demand recognition in ana- 

 tomical nomenclature. 



From time to time authors publish accounts and examples of the 

 sulcus post-centralis appearing in three pieces, instead of the classical 

 two. I believe the third piece in these cases to be either sulcus para- 

 cinguli or else sulcus praeparietalis. 



Connections of sulcus postcentralis superior. 



A sulcus which is very liable to become involved in this small 

 fissure-complex is the superior parietal. In all the figures save 1. C. 



Anat. An7. Bd. 44, Aufsätze. 7 



