16 Dr. Foville on the Anatomy of the Brain, 



nerves, inert conductors. It still remains to determine which 

 of these substances is pre-existent to the other ; in what or- 

 der the development of the different parts which they com- 

 pose takes place, and what are the most essential differences 

 in the nervous systems in different animals. It is sufficient 

 to mention the name of Tiedemann to remind you of the light 

 which has been thrown on these interesting and important 

 questions. 



I will not undertake to enumerate the many points which 

 are yet to be elucidated. I will merely, before exposing my 

 own views on the structure of the encephalon, allude to those 

 of the most eminent anatomists who have attempted to deter- 

 mine the disposition of the two substances composing the 

 encephalic masses. 



Willis, Malpighi, Reil, Gall, and Spurzheim are of opinion 

 that the white fibres of the crura cerebri, after emerging from 

 the medulla oblongata, penetrate into the hemispheres, di- 

 verging in various directions till they meet the gray matter of 

 the convolutions in which they terminate. They believe that 

 the corpus callosum reaching from one hemisphere to the 

 other is formed by the union on the median line of a new 

 order of fibres, originating in that same gray matter of the 

 convolutions, as that in which the fibres proceeding from the 

 crura cerebri terminate. Gall clearly and distinctly ex- 

 presses this opinion, when he says that the brain is formed 

 of two different orders of fibres, the one of diverging, the 

 other of converging fibres. 



Tiedemann does not admit these two orders of fibres. Ac- 

 cording to his views, the fibres meeting in the corpus callosum 

 are a continuation of those which proceed from the crura ce- 

 rebri after they have gone through the entire circumference 

 of the hemispheres. 



Which of these different views is consistent with the truth ? 

 Is there no other difficulty than the choice between them ? 



It is pretty generally admitted that the encephalic masses 

 are, according to the poetic language of Reil, " an efflores- 

 cence of the spinal marrow," the cerebrum being developed 

 at the summit of its anterior, the cerebellum, at the summit 

 of its posterior columns. The decussation between the two 

 anterior pyramids belonging to the anterior columns is held 

 to account for the effects of cerebral complaints being mani- 

 fested on the side of the body opposed to their seat in the 

 brain. 



For this last fact to be true, it is necessary that the decus- 

 sation between the two pyramids should be at once in com- 

 munication with all the muscular nerves in the body and with 



