THE FOEM-EELATIONS OF THE HUMAN BHAIN. 191 



ably give you a good idea of them, but they can never supply what is to be 

 gained by the study of the brain itself. 



We will now consider the convolutions and fissures of the surface of 

 the cerebrum. 



It is not so very long ago that anatomists manifested little interest, and 

 physicians none at all, in the study of the conformation of the cerebral 

 surface. Neither is it so very long since order was brought out of the seem- 

 ing chaos of the convolutions, and clear and accurate illustrations took the 

 place of those old plates concerning which an author pertinently remarked 

 that they resembled a dish of macaroni more than the brain. Interest was 

 first actively stimulated in regard to the human brain only after physiology, 

 followed shortly by pathology, had shown how differently irritations, extir- 

 pations, and diseases appear according as they involve this or that convolu- 

 tion of the hemisphere. 



It will be impossible to become as thoroughly acquainted with the course 

 of the convolutions as is desired, merely from descriptions and diagrams. 



Fig. 128. — Brain of a human foetus of the thirteenth week. 



Take a brain, therefore, and, following my description, trace out for your- 

 selves sulcus after sulcus and gyrus after gyrus. 



The hemispheres, primarily lens-shaped, grow out anteriorly and pos- 

 teriorly. In the middle only, at a point corresponding to the corpus striatum 

 within, the wall fails to follow this expansion as rapidly, and thus gradually 

 becomes more deeply situated. The fiat depression, which in this manner 

 arises on the stem of the hemisphere, is called the fossa Sylvii, and that part 

 which lies in the depression, the lobe of the st&m, or the insula Reilii. The 

 island is, therefore, that part of the cortex which adjoins the ganglia of the 

 cerebrum from without. At first it is entirely uncovered, but later is more 

 and more concealed by the expanding hemisphere overlapping it. 



This depression is easily found on the adult brain, likewise its posterior 

 continuation, the largest of the brain-fissures: the fissura Sylvii. If the 

 fissure is drawn apart, the island of Reil is discovered at the bottom tra- 

 versed by several perpendicular and oblique sulci. Even in the fifth month 

 of pregnancy two divisions of the Sylvian fissure, an anterior and posterior. 



