300 



THE BRAIN OF QUADRUMANA. 



In the Gorilla also, the External Perpendicular Fissure 

 (fig. 117, s c) is very distinct and long, its hinder margin 

 (Operculum) being convex anteriorly, and somewhat more 

 sinuous than it is in the Chimpanzee. The first ' bridging 

 convolution ' emerges from beneath it above. But in the 

 Orang this Perpendicular Fissure is sometimes much 

 shorter and less obvious (fig. 119) than it is in either of 

 the other two great Apes, so that in this respect its brain 

 approaches more closely to that of Man. It is sometimes 



interrupted above by 

 an upper ' bridging 

 convolution ' which 

 has a superficial posi- 

 tion of this kind in 

 no other of the Quad- 

 rumana, except in 

 Ateles. 



According to Rolle- 

 ston this superficial 

 position of the upper 

 or first ' bridging con- 

 volution ' is not con- 

 stant in the Orang or 



FIG. 119. Brain of Orang, upper aspect. (Duncan, even in Man while 



from specimen in Museum of Royal College of Bur- j n both it HiaV at 

 geons.) F, Frontal Lobe ; O, Occipital Lobe. * 



times be present on 



one side and absent on the other. He adds : " In the 

 higher species of the order Apes, as in the higher varieties 

 of the species Man, we find variability the rule, uniformity 

 the exception ; in the lower species, as in the lower varie- 

 ties of Man, the reverse condition obtains." 



The second ' bridging convolution ' which is always 

 present, superficial and easily recognizable in Man, is said 

 to be as invariably absent in the Chimpanzee and the 



