THE NERVOUS SYSTEM 



The trapezoid body (corpus trapezoideum) , which in most mammals appears 

 on the surface of the medulla near the border of the pons (Fig. 83), is covered 

 in man by the enlarged pars basalis pontis. In sections through the more caudal 

 portions of the pons the trapezoid body forms a conspicuous bundle of trans- 

 verse fibers in the ventral portion of the reticular formation (Fig. 108). The 

 fibers are associated with the terminal nuclei of the cochlear nerve, especially 

 the ventral one, and with the superior olivary nucleus, around the ventral border 

 of which they swing in such a way as to form a bay for its reception. Farther 

 medialward they pass through the medial lemniscus at right angles to its con- 



Fourth ventricle 

 Stria medullares 



Dorsal cochlear nucleus 



Vent, spinocerebellar tract 



Vent, external arcuate fibers 

 Medial lemniscus 



Nucleus of eminentia teres 



Principal vestibular nucleus 



Lateral vestibular 

 nucleus 



Nucleus of tract us 

 solitarius 

 Glossopharyngcal 



nerve 

 Dorsal cochlear 



nucleus 



Restiform body 

 Ventral cochlear 

 nucleus 



Spinal tract and 

 nucleus N. V 



Trapezoid body 

 Pontobulbar body 

 Medial longitudinal fasciculus 

 Thalamo-olivary tract 



Inferior olivary nucleus 

 Pyramid, corticospinal tract 

 Arcuate nucleus 



Foramen cacum Pons 



Fig. 107. Section through caudal border of the pons and the cochlear nuclei of a child. 



Weigert method. ( X 4.) 



Pal- 



stituent fibers and decussate in the median raphe. The trapezoid body de- 

 scribes a curve with convexity directed rostrally as well as ventrally, and as a 

 result its lateral portions are seen best in sections through the lower border 

 of the pons (Fig. 107), while the rest of it is in evidence in sections at a higher 

 level (Fig. 108). Arising from the ventral nucleus of the cochlear nerve (Fig. 

 107) these fibers pass, with or without interruption in the superior olivary 

 nucleus, across the median plane (Fig. 108) ; and, on reaching the lateral border 

 of the opposite superior olivary nucleus, they turn rostrally to form a longi- 

 tudinal band of fibers known as the lateral lemniscus (Fig. 110). This is a 



