BRAIN OF MAN AND THE BRAINS OF CERTAIN ANIMALS. 43 



lobe i and 3. They are very generally present in human brains, 

 and in highly convoluted brains they often are especially highly 

 convoluted also. Their classificatory importance I should not rank 

 so highly, partly because one or other of them, or both, may be 

 possessed by apes, and the mass lettered a and ft may come out 

 to the surface in them, forming, it is true, an hourglass-shaped 

 lobe, not a sub-quadrate one, as in man, but coming up to the 

 surface for all that, partly because they are not invariably present 

 in such full development as M. Gratiolet's words would imply, and 

 partly because they are, in a morphological point of view, tertiary 

 convolutions, latest to be developed, and most liable to variation 

 (Reichert, * Gehirn,' p. 89, ii. Abtheilung). The history of these 

 convolutions amongst certain of the lower apes becomes exceedingly 

 instructive. The arrangement and relative development of them 

 differ most widely in two of the commonest American monkeys, 

 which are so closely related as to have been confounded together 

 by certain zoologists. I mean the Brown Sagow, or Weeper 

 Monkey (Cebus apella), and the Cebus capucinus, Fatuellus, or 

 Horned Monkey. Will anybody pretend that any difference can 

 be detected in the psychical phenomena, the mental manifestations, 

 of these creatures, at all in correspondence or concomitant variation 

 with their difference of cerebral conformation ? Why Linnseus 

 named the Cebus capucinus * Cebus fatuellus ■,' I know not ; if it 

 were really for fatuity, that fatuity existed in connexion with a 

 brain which, so far as I can see, was superior to that of its rival, 

 the Cebus apella. 



Lastly, the fissure in which these conditions exist, either filling 

 it up level with either edge, or winding down into its depths and 

 up its declivities, has an internal aspect, and this internal aspect 

 may present the chasm appearance, or it may be filled up. In man 

 it is always a chasm, it is never filled up. Two convolutions, the 

 internal connecting bridges, are as invariably, and more invariably, 

 if so I may say, atrophied and concealed in this place in man, than 

 the external are in apes. In many of the monkeys, and they too 

 not often highest in their class, this internal chasm is filled up. In 

 the diagrams these facts are shown, though I must own somewhat 

 indistinctly. In the monkey's brain (Fig. 1 b, I.) this internal fissure 

 is irregularly seamed, and not smooth as in the human brain. 

 Now the irregular seaming is due to the transverse section of an 



