n MAMMALIA: BRAINS. 133 



very few grooves, which are technically termed 

 " sulci," separating ridges or " convolutions " of 

 the substance of the brain; and the smaller species 

 of all orders tend to a similar smoothness of brain. 

 But, in the higher orders, and especially the larger 

 members of these orders, the grooves, or sulci, 

 become extremely numerous, and the intermediate 

 convolutions proportionately more complicated in 

 their meanderings, until, in the Elephant, the 

 Porpoise, the higher Apes, and Man, the cerebral 

 surface appears a perfect labyrinth of tortuous 

 foldings. 



"Where a posterior lobe exists and presents its 

 customary cavity — the posterior cornu — it com- 

 monly happens that a particular sulcus appears 

 upon the inner and under surface of the lobe, 

 parallel with and beneath the floor of the cornu — 

 which is, as it were, arched over the roof of the 

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

 indenting the floor of the posterior horn from with- 

 out with a blunt instrument, so that the floor 

 should rise as a convex eminence. Now this 

 eminence is what has been termed the " Hippo- 

 campus minor; " the " Hippocampus major " being 

 a larger eminence in the floor of the descending 

 cornu. What may be the functional importance 

 of either of these structures we know not. 



As if to demonstrate, by a striking example, the 

 impossibility of erecting any cerebral barrier be- 



