■ TO THE LOWEE ANIMALS. 115 



tliat a particular sulcus appears upon the inner and under 

 surface of tlie lobe, parallel with and bSieath the floor of 

 the cornu — wliich is, as it were, arched over the roof of 

 the sulcus. It is as if the groove had been formed by in- 

 denting the floor of the posterior horn from without with 

 a blunt instrument, so that the floor should rise as a con- 

 vex eminence. I^ow this eminence is what has been 

 termed the ' Hippocampus minor ; ' the ' Hippocampus 

 major' being a larger eminence in the floor of the de- 

 scending cornu. What may be the functional importance 

 of either of these structures we know not. 



As if to demonstrate, by a striking example, the im- 

 possibility of erecting any cerebral barrier between man 

 and the apes, l^ature has provided us, in the latter ani- 

 mals, with an almost complete series of gradations from 

 brains little higher than that of a Rodent, to brains little 

 lower than that of Man. And it is a remarkable circum- 

 stance, that though, so far as our present knowledge ex- 

 tends, there is one true structural break in the series of 

 forms of Simian brains, this hiatus does not lie between 

 Man and the man-like apes, but between the lower and 

 the lowest Simians ; or, in other words, between the old 

 and new world apes and monkeys, and the Lemurs. 

 Every Lemur which has yet been examined, in fact, has 

 its cerebellum partially visible from above, and its poste- 

 rior lobe, with the contained posterior cornu and hippo- 

 campus minor, more or less rudimentary. Every Marmo- 

 set, American monkey, old world monkey. Baboon, or 

 Man-like ape, on the contrary, has its cerebellum entirely 

 hidden, posteriorly, by the cerebral lobes, and possesses a 

 large posterior cornu, with a well developed hippocampus 

 minor. 



In many of these creatures, such as the Saimiri {Chry- 



