202 Royal Irieh Academy. 



examined. luto those elaborate details I do not enter ; but the 

 general conclusion at which he arrives is of great importance — it is 

 that the several sulci appear, on the average, in the following order — 

 first, the sulcus praecentralis inferior and the second frontal furrow ; 

 then the lower portion of the sulcus prsecentralis superior, with the 

 basal part of the first frontal furrow ; and afterwards, in succession, the 

 anterior part of this last with the upper part of the sulcus prsecentralis 

 superior ; next the sulcus frontalis medius ; and lastly the sulcus 

 frontalis mesialis. It would be natural to suppose that this order 

 represents the relative degrees in which those sulci are stamped on the 

 structure of the primate brain generally ; but, in order to ascertain 

 this, the question of the homologues of these several furrows in the 

 simian cerebrum must first be determined. Dr. Cunningham goes into 

 a most careful study of the sulci in the ape cerebrum from Cebus up 

 to the anthropoids, and, differing from some of his most eminent 

 predecessors, he arrives at the following conclusions. 



The sulcus frontalis inferior in man, he holds (with Gratiolet), 

 corresponds in the apes with what Mingazzini has called the sulcus 

 rectus, which already appears in Cebus. The sulcus praecentralis inferior 

 corresponds to the sulcus arcuatus which is well seen in Callithrix. 

 The sulcus frontalis primus is of comparatively late origin, and is 

 absent in some of the lower apes ; when it appears, it is represented 

 by certain shallow furrows which lie between the horizontal part of 

 the sulcus arcuatus and the mesial border of the hemisphere. The 

 hindermost of these, Dr. Cunningham thinks (so far agreeing with 

 Eberstaller), may be a sulcus prsecentraKs superior. Lastly, the sulcus 

 frontalis mesialis, which, in man, divides the superior frontal convolu- 

 tion into two, does not appear in the simian cerebrum at all, and is less 

 strongly marked in the lower than in the higher human races. Thus 

 the ontogenetic and phylogenetic evidences agree in fixing the order 

 of importance of these frontal furrows. 



Another alleged homology is discussed by Dr. Cunningham. The 

 sulcus fronto-orbitalis has been regarded as representing in the anthro- 

 poids the anterior limb of the fissure of Sylvius. This he shows to be 

 an error, arising from neglect of the fact, already mentioned, that 

 there is no frontal and no orbital operculum in the anthropoids, a 

 portion of the insula in them being exposed on the surface which 

 in man is submerged. There is no anterior Sylvian limb in the 



