278 



FUNCTIONS OF THE NERVOUS SYSTEM. 



then found, that these fibres may be traced upwards, chiefly into the Corpora 

 Striata, whence they radiate to the Hemispheres ; and downwards, chiefly into 

 the Anterior Pyramids. From this tract arise all the Motor nerves usually 

 reckoned as Cranial; as will be seen in the accompanying Figure. The 

 Sensory tract is displayed, by opening the Medulla Oblongata on its posterior 

 aspect ; and then separating and turning aside the Restiform Columns, so as 

 to bring into view the Posterior Pyramids, which lie on the outside of the ca- 

 lamus scriptorius. On tracing their fibres upwards, it is found that they form 

 a part of the posterior layer of the Crura Cerebri, ultimately passing on to the 

 Thalami optici, whence they radiate to the Hemispheres. From this tract, 

 no motor nerves arise ; but on tracing it downwards into the Spinal Cord, it 

 is found that the sensory root of the fifth pair terminates in it, and that the 



Fig. 141. 



= o 



Course of the Sensory tract according to Sir C. Bell. A. Pons Varolii ; B, B, sensory tract separated ; 

 c, union and decussatiou of posterior columns ; D, D, posterior roots of spinal nerves ; E, sensory roots of 

 fifth pair. 



posterior roots of the spinal nerves are evidently connected with its continua- 

 tion. Also forming part of the posterior division of the crus cerebri, and se- 

 parated from the anterior by the transverse septum, is a layer of fibres which 

 ascends from the Olivary bodies, some of which terminate in the Corpora 

 Quadrigemina. 



352. On tracing upwards the four divisions of the Medulla Oblongata, the 

 following are found to be their chief connections with the Brain. 1. The 

 fibres of the Anterior Pyramids for the most part enter the Crura Cerebri, 

 passing through the Pons Varolii, and traversing the Optic Thalami (which, 

 it must be carefully borne in mind, have scarcely any real connection with 

 the Optic Nerves, or with the sense of sight) ; after which they diverge and 

 become intermingled with grey matter, thus forming the Corpora Striata, and 

 finally radiate to the convolutions of the Cerebrum. 2. The fibres of the 

 Olivary body also pass into the Pons Varolii, and there divide into two bands ; 



