- SIR CHARLES BELL ON THE BRAIN. 475 



transverse laminae of fibres above alluded to, one superficial and the other deep-seated. 

 We observe also an oblique lateral process which passes from the cerebellum to the 

 crus cerebri. These septa intersect and distinguish the grand fasciculi or tracts of 

 nervous matter, which, coming down from the cerebrum, seem to flow under the 

 bridge and converge in the medulla oblongata*'. 



We commence our investigation with parts that are familiar. We trace the cor- 

 pora pyramidalia of the medulla oblongata upwards from the point of their decussa- 

 tion towards the brain. They enter the pons by two distinct arches. The superficial 

 layer of transverse fibres stretching from the crura cerebelli is over them, and the 

 deeper septum is under them. On raising the superficial layer of the pons, we see 

 the fibres of the corpora pyramidalia passing quite through to the crus cerebri ; and 

 now in one view we see a great portion of the grand tract which furnishes the nerves 

 of motion (Plate XIX. a. b. c). 



Let us divide these tracts by a transverse incision where the corpora pyramidalia 

 enter the pons, and lift them up. We keep close to the deeper transverse septum, 

 which we shall find as distinct and smooth as a floor, and now directed by this 

 septum we distinguish the portion of fibrous matter which is anterior to it ; and if 

 we follow this up into the crus cerebri, we shall come upon the corpus nigrum, and 

 find that the crus is not a simple texture of filaments, but that it is compound, and 

 that we are lifting that anterior division of it which belongs to motion, and which 

 we shall find spreads over the tract of nervous matter which comes up behind the 

 deeper-seated septum. 



We may complete our view of this motor tract, by making sections of the cere- 

 brum, and pursuing the diverging fibres, first into the corpus striatum, and thence, 

 as they proceed onwards, spreading into the hemisphere of the cerebrum and diver- 

 ging to the cineritious convolutions. 



Thus we have already found, that the crus cerebri is not simple, but consists of 

 parts easily and naturally divided. Returning then to the pons as furnishing us with 

 the means of making the natural distinctions of these tracts, we take the deep sep- 

 tum or posterior set of transverse fibres again as our guide, and trace 



The posterior Tract. 



To obtain a distinct view of the whole extent of the posterior tract, we require to 

 have the parts carefully prepared -}-. It will be very convenient to have the crura, pons, 



* The terms pons and nodus are sufficiently intelligible and harmless, as implying no theory ; I retain the 

 old names unless the new ones be countenanced by the just eminence of the authors who have invented them. 

 This is the proper check against the mutiplication of terms in anatomy. In describing the course of the fibres, 

 the expressions I employ are used in their anatomical sense, as implying the direction in which the hand and 

 eye are following the line, and not in reference to the course in which I may suppose the energy to pass in the 

 performance of their functions. 



t It will be in vain for the anatomist to attempt demonstrating these facts in the recent brain ; but he will 

 find it easy if he take some old preparation of the brain, which has been for some years in spirits. 



