THE MEDULLA OBLONGATA AND TEGMENTUM OF THE PONS. 205 



Iii our upward progress we have now reached the point 

 where the lowest fibres of the pons, running across the pyramids 

 from the cerebellum, appear at the ventral periphery of the 

 section. 



Here we strike a region where several important structures 

 are compressed into a relatively small space, the region of the 

 origin of the acoustic, the facial, and the abducens nerves. 



In the section represented in Fig. 122 you see that from 

 the ventral nucleus of the acoustic there arises a root composed 

 of fine fibres. This is the radix posterior acustici. You will 

 also notice that another tract runs upward from this same nucleus 

 and in part enters a rounded nucleus, the superior olivary body, 



Y. <?6(A/CO(/S 



FIG. 123. FIG. 124. 



Medulla oblongata and pons of an ape. Diagram of the central course of the 



To show the corpus trapezoides. facial and abducens nerves. 



Knie, Knee. 



and in part extends, over the median line. These latter fibres 

 pass transversely through the layer of the fillet, which is placed 

 in the dorsal portion of the pons. In the lower animals, where 

 the pons is much shorter than in human beings, this tract can 

 be seen as a quadrangular medullary area passing across the 

 pyramids in the ventral portion of the oblongata. This area 

 and the fibres it contains have received the name of corpus 

 trapezoides. 



The fibres in the corpus trapezoides connect the ventral 

 acoustic nucleus with the superior olivary body of the same and 

 of the opposite side. This is made clear in the following cut 

 (Fig. 125). 



