LECTURE IV. 



THE CONVOLUTIONS AND FISSURES OF THE SURFACE OF THE 



CEREBRUM. 



GENTLEMEN : It is not so very long ago that the study of 

 the structure of the brain surface possessed very little interest 

 for the anatomist and none at all for the practicing physician. 

 Nor is it a very long time since order was brought out of the 

 seeming chaos of the convolutions of the brain, so that clear and 

 definite cuts have taken the place of the old plates, concerning 

 which an author pertinently remarked that 

 they were a better representation of a dish of 

 macaroni than of the brain. Interest was first 

 awakened in regard to the human brain after 

 physiology and pathology had shown the dif- 

 ferent results of irritation, extirpation, and Brain /i^ n f an embryo 

 disease, varying according to the different i* 

 convolutions attacked. It is, therefore, of importance, gentlemen, 

 that you learn to know thoroughly the arrangement of these con- 

 volutions and the course of the fissures which separate them. 

 By word and diagram alone it will be impossible for me to make 

 you as thoroughly acquainted with these structures as you should 

 be. Here again it is necessary for you to take a fresh brain, 

 and, following my lecture, trace out for yourselves sulcus after 

 sulcus and convolution after convolution. 



The primarily lens-shaped hemispheres grow, as you know, 

 toward the front and backward. Only in the middle, at a point 

 corresponding to the corpus striatum within, the surface does 

 not expand as rapidly, and, hence, becomes more depressed than 

 the surrounding parts. The depression which thus exists near 

 the point of origin of the hemispheres is called the fossa or 

 fissure of Sylvius, and that part which lies in the depression the 



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