130 



FUNCTIONS OF THE NERVOUS SYSTEM. 

 Fig. 24. 



Course of the Sensory tract after Sir C. Bell. A, pons varolii ; B. B, sensory tract separated ; c, union and 

 decussaiion of posterior columns ; D, D, posterior roots of spinal nerves ; E, sensory roots of fifth pair. 



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

 following are found to be their chief connections with the brain. 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 by the student, have no real connection with the 

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

 come intermingled with gray matter, thus forming the Corpora Striata, and 

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

 body also pass into the Pons Varolii, and there divide into tw r o bands, of which 

 one proceeds upwards and forwards to join the Crus Cerebri, whilst the other 

 passes upwards and backwards into the Corpora Gluadrigemina. Of the true 

 Restifdrm bodies, the fibres pass entirely into the Cerebellum. Finally, of the 

 Posterior Pyramids, the fibres pass directly onwards through the Crura Cerebri 

 into the Thalami, whence they radiate to the convolutions. 



171. The downward course of these fibres into the Spinal Cord now re- 

 mains to be traced; and their arrangement is by no means a simple one. The 

 anterior Pyramids decussate, as is well known, at their lower extremity ; the 

 principal part (but not the whole) of the fibres on each side, passing over to 

 the other. The decussating fibres pass backwards as well as downwards, and 

 enter, not the anterior column of the spinal cord (as commonly stated), but 

 the middle column.* The smaller bundle of fibres, which do not decussate, 

 passes downwards, along with those of the olivary bodies, to form the anterior 

 column. The fibres descending from the Olivary bodies converge, as those of 

 the pyramids pass backwards from between them, until they meet on the 

 median line, forming the greater part of the anterior column. The fibres of 



* See Dr. J. Reid, in Edinb. Med. and Surg. Journal, Jan., 1841. 



