LECTURE IV. ' 103 



wticli is not visible externally. It may be seen by separating- 

 the margins of the Sylvian fissure, and removing parts of the pa- 

 rietal lobe which cover it. Though the formation of this inter- 

 mediate lobe seems peculiar to the cerebral sti-ucture of man 

 and the ape, not having, to our knowledge, been met with in 

 other animals, it need not further occupy our attention, since 

 the comparative anatomy of the brain, as far as races are con- 

 cerned, is as yet in its infancy. 



Many attempts have been made to connect the development 

 of the several cerebral lobes with the^ mental qualification 

 of individuals and races, but with scanty success. The three 

 cranial vertebrte, namely, the frontal, temporal, and occipital, 

 have been connected with the development of the three prin- 

 cipal lobes, so that some authors distinguish frontal, pai"ietal, 

 aud occipital races, in proportion as either of these regions 

 predominate. Some have proceeded still further, naming the 

 races, — "Men of the day, men of the twilight, and men of 

 the night," with the very acute remark that the forehead of 

 man corresponded to day ; but the occiput to the shady or 

 night side of nature. Even north pole and south pole, and 

 the point of magnetic indifference, have played their parts in 

 these vertebral theories ; from the analyses of which I must 

 beg to be excused, as the times in which we live are not much 

 given to such speculations as these. The actual facts obtained 

 from investigations of the kind seem to amount to this, that 

 the anterior or frontal lobes are intimately connected with 

 mental development. Height, breadth, and shape of this part 

 must be taken into special consideration in forming an esti- 

 mate of intellectual capacity. 



The development of the convolutions on the surface of the 

 brain is of particular importance. As already observed, the 

 whole surface of the cerebrum is covered with a layer of grey 

 matter, beneath which the white substance appears. If the 

 convolutions are broad, the white substance penetrates to 

 their centre ; if small or imperfect, they are formed wholly of 

 grey matter. The very delicate vascular membrane which 

 covers the brain enters into the sulci. The dura mater is 

 stretched over the convolutions, so that the internal surface of 



