SENSE AREAS AND ASSOCIATION AREAS. 215 



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. 95). 

 Some strike directly across toward the ventral 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 corpus trapezoideum. The 

 fibers of this cross band end, according to some observers, in 

 certain nuclei 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 auditory fibers enter a distinct tract long known to the anat- 

 omist and designated as the lateral fillet or lateral lemniscus. 

 Authors differ as to whether the auditory 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 without ending and then bend to run for- 

 ward in a longitudinal direction. This last view is represented 

 in the schema (Fig. 95). 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 form a structure 

 visible to the eye and known as the medullary or auditory striae. 

 The fibers of this system dip inward at the raphe, cross the 

 mid-line, and a part of them at least eventually reach the lateral 

 lemniscus of the other side either with or without ending first 

 around the cells of the superior olivary nucleus. According to 

 the description of some authors, the fibers from the accessory 

 nucleus and tuberculum acusticum do not all cross the mid-line 

 to reach the lateral lemniscus of the other side; some of them 

 pass into the lateral lemniscus of the same side; so that the 

 relations of the fibers of the cochlear nerves to the lateral lemnis- 

 cus resemble, in the matter of crossing, the relations of the optic 

 fibers to the optic tract. After entering the lateral lemniscus 

 the auditory fibers pass forward toward the midbrain and end 

 in part in the gray matter of the inferior colliculus and in part in 

 the median or internal geniculate, and, according to Van Gehuch- 

 ten, partly also in a small mass of nerve cells in the midbrain known 



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

 8, 127, 1906. 



