LECTURE III. 



THE GENERAL CONFORMATION AND HISTOLOGY OF THE BILUN. 



GENTLEMEN: Although these lectures are not addressed 

 to beginners, but to those who have a general acquaintance 

 with the coarser anatomy of the brain, it will not be entirely 

 superfluous to review our knowledge and to form a clear image 

 of brain-structure in our minds. The outlines of the map in 

 which, later, we intend to mark out all the points and by-ways 

 which are of importance, will be definitely fixed by a recapitula- 

 tion of what has already been learned. Taught by embryology, 

 you will easily understand the morphological conditions presented 

 by the organ of the adult individual. 



A fresh brain is laid on its base. You will easily discover 



t/ 



the great fissure which separates the two hemispheres and the 

 fissure of Sylvius which was originated by the growth of the 

 temporal lobe. Inasmuch as the hemispheres have grown over 

 most of the other portions of the brain (Fig. 5), we could get a 

 view of the latter posteriorly by raising up the hemispheres and 

 uncovering them. This could also be accomplished by removing 

 a portion of the hemispheres. The latter method has the ad- 

 vantage of giving us a view of the lateral ventricles and the 

 corpus striatum, and we will therefore follow it. 



The knife held horizontally passes through both hemi- 

 spheres at once and removes layers from 2 to 3 millimetres 

 in thickness. The first and second of these layers contain much 

 cortical matter and relatively little of the inclosed white sub- 

 stance ; but in removing the third layer we have uncovered a 

 large white field of medullary matter in the middle of each liemi- 



J 



sphere, the centrum semiovale. In it run all those fibres which 

 pass from the cortex downward, and a part of those fibres which 

 connect the different portions of the cortex with one another. 



(31) 



