SENSE AREAS AND ASSOCIATION AREAS. 213 



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 anatomist and 

 designated as the lateral fillet or lateral lemniscus. The sensory 

 fibers that arise ■ in the doi-sal nucleus 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 authoi-s, the fibers from the two auditory 

 nuclei do not all cross the midline 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 lemniscus 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 coUic- 

 ulus and in part in the median or internal geniculate, and, accord- 

 ing to Van Gehuchten, partly also in a small mass of nerve cells 

 in the midbrain known as the superior nucleus of the lemniscus. 

 From this second or third termination another set of fibers, the 

 auditory radiation, continues forward through the inferior ex- 

 tremity of the internal capsule to end in the superior temporal 

 gyrus (see Fig. 82, E). The median geniculates, in man at least, 

 have the function of a subordinate auditory center, as the lateral 

 geniculates have the function of a subordinate visual center. The 

 median geniculates are connected with the inferior colliculus, and 

 also, it will be remembered, with each other, by commissural 

 fibers (Gudden's commissure) that pass along the optic tracts and 

 the inferior margin of the chiasma. The auditory path, there- 

 fore, involves the following structures: The spiral ganglion, the 

 cochlear nerve, accessory nucleus and tuberculum acusticum, 

 corpus trapezoideum, medullary striae, superior olivary, lateral 

 lemniscus, inferior colHculus, median geniculate, Gudden's com- 

 missure, auditory radiation, and temporal cortex. 



The Olfactory Center. — The olfactory sense is quite un- 

 equally developed in different mammals. Broca divided them from 

 this standpoint into two classes: the osmatic and the anosmatic 



