SIR CHARLES BELL ON THE BRAIN. 483 



Plate XX. 



Fig. 1 . Represents the plates of fibres which pass across the pons and medulla ob- 

 longata, and which divide those great columns of medullary matter 

 which we trace down from the cerebrum into the spinal marrow. 



A, A. The posterior transverse septum of the pons, seen from the back part. 



B. The septum, which rising perpendicularly from the septum of the pons, 

 divides the great tracts of nervous matter which descend from the cere 

 brum, viz. the posterior divisions of the crura cerebri. 

 c, c. The lateral septum of the medulla oblongata, which separates the corpus 

 olivare from the anterior or muscular tract. 

 Fig. 2. In this figure the posterior or sensitive tract is shown. They are separated 

 so as to exhibit the posterior transverse septum of the pons. 

 A. The pons Varolii, with the transverse fibres of the septum (fig. 1. a, a.). 



B, B. The sensitive tract dissected and separated. 



c. The union and decussation of the posterior tract. 



D, D. The posterior root of the spinal nerve continued with the posterior tract 



below the decussation. 



E, E. The sensitive roots and tracts of the fifth pair of nerves. 



Plate XXI. 



This figure presents a lateral view (slightly oblique) of the two columns, with a 

 section of the pons and crus cerebri. 



A. Fibrous texture of the anterior tract as it converges from the left hemi- 



sphere of the cerebrum. 



B. A section of the left crus cerebri. 



c. The motor tract in its course through the pons Varolii. 

 D. The corpus pyramidale of the left side. 

 E, E. The posterior or sensible tracts. 



F. Their union and decussation. 



G. The corpus olivare, hanging by the tract or column, where it is united to 



the anterior column d and the posterior column e. 

 H. The superior part of the tract of the corpus olivare, running up into the 



corpora quadrigemina. 

 I. Corpora quadrigemina. 



Note. — ^These views of the brain have been taken from dissections made of the 

 parts after they have been preserved a long time in proof spirits. 



