OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



guishable externally from the Restiforrn bodies, of which they were formerly 

 described as a constituent part; they, however, form the immediate boundaries 

 of the posterior median fissure; and whilst superficially marked-off from the 

 E-estiform bodies by a slight groove, are more completely separated from them 

 by their anatomical relations to the parts above and below. Their fibres estab- 

 lish a connection between the sensory tract (Fig. 178, st, st) of the Crura 

 Cerebri, and the posterior part of the lateral columns of the Spinal Cord, some 

 of them passing also into its posterior columns. These fibrous tracts are stated 

 by Mr. Solly 1 and Dr. Radclyfie Hall 3 to decussate, partially at least, whilst 

 passing through the Pons Varolii. 3 The gray nuclei of the Posterior Pyramids, 

 situated immediately beneath the "fourth ventricle" (which is nothing else 

 than the space left by the divergence of the Restiform and Posterior Pyramidal 

 tracts), are the ganglionic centres of the Auditory nerves, or the proper Audi- 

 tory ganglia; and it is interesting to observe that their seat precisely corre- 

 sponds with that of the rudimental organ of hearing in many Invertebrata. 



712. The Medulla Oblongata is usually considered as terminating at the 

 lower border of the Pons Varolii ; but it will be convenient here to trace up- 



Fig. 181. 



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

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



wards the strands by which it is connected with the higher Encephalic centres, 

 as a clearer idea of its anatomical and physiological relations will thus be ob- 

 tained. The Pons is chiefly composed of transverse fibres which constitute the 

 great commissure of the Cerebellum ; and these fibres not only surround the 



1 "The Human Brain," 2d edit., p. 243. 



2 "Edinb. Med. and Surg. Journ.," July, 1847, Plate vn. 



3 A decussation of the Posterior Pyramids was described by Sir C. Bell as occurring at 

 the same level with the decussation of the Anterior Pyramids (Fig. 133, c) ; there can be 

 no doubt, however, that this is an error, which probably originated in his having misin- 

 terpreted the appearance presented by the posterior aspect of the anterior decussation. 



