141 



of a sagittal section 2 cm from the mesial plane. The asterisk (■'^) 

 represents the groove occupied by the ala parva of the sphenoid. 

 Contrary to the opinion of Spitzka, this groove may become a de- 

 finite sulcus in those cases in which the limbus is very large. 



Cor^wi itT«.*i»*i»^ 



Lv-mbus "po start »toi is 



Tiii. pylvU 



Figure reprt'sentiug the basal part of a sagittal section through the Ijrain of an 

 Egyptian Fellah, 2 cm from the mesial plane. * Sulcus alae parvae. X '%• 



At first I was inclined to regard this groove as the result of the 

 post mortem action of gravity on the soft brain mass; but a careful 

 examination of brains hardened in situ often shows two equally well- 

 preserved hemispheres (which of course would be equally exposed to 

 the action of gravity), one possessing a large limbus, the other with none. 



Moreover, I have seen (on the left side of the head of a Syrian) 

 a prominent crest on the alisphenoid occupying the Sylvian fissure, 

 which was 1 cm behind the orl)ito-sphenoid. 



In the early developmental history of the head the Sylvian region 

 of the brain and the sphenoid part of the cranium become mutually 

 moulded the one to the other. In the subsequent period, when the 

 form of the sphenoid is fixed, the orbital operculum, as it grows back- 

 ward, may cross from the anterior into the middle cranial fossa and 

 thus form the limbus postorbitalis, which becomes marked oft' from the 

 rest of the orbital region by the groove produced by the orbito-sphenoid. 



