200 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



restiform body and known as the ventral or accessory nucleus 

 (V.n., Fig. 90), and one dorsally, known as the dorsal nucleus or 

 the tuberculum acusticum (D.n.). From these nuclei the path 

 is continued by secondary sensory neurons, and its further 

 course toward the brain is still a matter of much. uncertainty 

 in regard to many of the details.* The general course of the 

 fibers, however, is known. Those axons that arise from the 

 accessory nucleus pass mainly to the opposite side by slightly 

 different routes (Fig. 90). Some strike directly across toward the 

 vental side of the pons, forming a conspicuous band of transverse 



fibers that has long been 

 <* known as the corpus 



trapezoideum ; others 

 pass dorsally around 

 the restiform body and 

 then course downward 

 through the tegmental 

 region to enter the cor- 

 pus trapezoideum. The 

 fibers of this cross band 

 end, according to some 

 observers, in certain nu- 

 clei of gray matter on the 

 opposite side of the pons, 

 especially in the superior 

 olivary body and the 

 trapezoidal nucleus, and 

 thence the path forward 

 is continued by a third 

 neuron. Certainly from 

 the level of the superior 

 olivary body the audi- 

 tory fibers form a dis- 

 tinct band long known 

 to the anatomist and des- 

 ignated as the lateral fillet or lateral lemniscus. Authors differ 

 as to whether the fibers of this tract arise from nerve cells in the 

 superior olivary and neighboring nuclei, or are the fibers from the 

 accessory nucleus which pass by the superior olivary body with- 

 out ending and then bend to run forward in a longitudinal direc- 

 tion. This last view is represented in the schema (Fig. 90). The 

 secondary sensory fibers that arise in the tuberculum acusticum 

 pass dorsally and then transversely, forming a band of fibers that 

 comes so near to the surface of the floor of the fourth ventricle as to 

 * For literature see Van Gehuchten, "Le Nevraxe," 4, 253, 1903. 



Fig. 90. Diagram to show central course of 

 auditory fibers (modified from Van Gehuchten) : 

 D.n., Dorsal nucleus giving rise to the fibers that 

 form the auditory stria? (a.s.); V.n., the ventral nu- 

 cleus, giving origin to the fibers of the corpus trape- 

 zoideum (,c.tr.); s.o., superior olivary nucleus; l.f., 

 lateral fillet; n.s., nucleus of the lateral fillet; t.g.i., 

 the inferior colliculus. 



