444 PHYSIOLOGICAL BBBIBB, 



will be found that tin* fundamental plan of the orliital 

 sulcu> (which is that often called " presvlvian " in other 

 mammals) is that exhibited on the right hfini-pheiv <>f 

 this Gorilla's brain. In the other three Gorilla-brains, 

 different variants of this plan of orbital are exhibited. 



The peculiar bifurcation of the termination of the Sylvian 

 fissure, which is such a constant feature of the Orang's 

 brain, is very poorly developed on the right hemisphere of 

 this, and even less distinctly in the two hemispheres of 

 specimen D. 659. The central sulcus exhibits a very 

 distinct genu. 



On the right hemisphere there is a typical primitive 

 sulcus arcuatus (inferior precentral) such as the Apes 

 exhibit. There is a long bow-shaped sulcus rectus, which 

 joins the mesial accessory-orbital sulcus in front. A short 

 branch of the " straight " sulcus passes between the dorsal 

 ends of the orbital and fronto-orbital sulci. On the left 

 hemisphere, the oblique upper limb of the arcuate seems 

 considerably curtailed and its lower end passes (super- 

 ficially) into the central sulcus. Moreover, the upper part 

 of the sulcus is linked by a short deep branch to the sulcus 

 rectus. If the reader compares this specimen with those 

 of the Orang and notes the relations of the sulci to the 

 fronto-orbital sulcus, he cannot fail to understand why the 

 anterior limb of that peculiar H-shaped frontal system of 

 furrows, which is so characteristic of the Orang, was called 

 (in these notes) the posterior part of the " sulcus rectus " 

 (the inferior frontal of Human Anatomy). On the left 

 hemisphere a small cephalic element of the *' rectus " series 

 has become separated to form a frOHto-marginal sulcus <>l 

 Wernicke. In both hemispheres, tin 1 superior precentral 

 and superior frontal sulci are arranged with a simplicity 

 and regularity which is quite diagrammatic. 



On the left hemisphere there is a short "sulcus frontalis 

 medius," placed very far forward between the anterior 

 ends of the superior and interior frontal sulci. On the 

 right hemisphere there is a short, almost coronal sulcus in 

 the same region. 



When we recall how constant in the Orang's brain is the 

 presence of an inferior transverse sulcus (superficially) 



