SENSE AREAS AND ASSOCIATION AREAS. 203 



are the fibers from the accessory nucleus which pass by the superior 

 olivary body without ending and then bend to run forward in a 

 longitudinal direction. This last view is represented in the schema 

 (Fig. 89). The secondary sensory fibers that arise in the tubercu- 

 lum 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 f , mid-line, and a part of them at least 

 eventually reach the lateral fillet 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 fillet of the other side; some of them 

 pass into the lateral fillet of the same side; so that the relations of 

 the fibers of the cochlear nerves to the lateral fillet resemble, in the 

 matter of crossing, the relations of the optic fibers to the optic 

 tract. After entering the lateral fillet the auditory fibers pass 

 forward toward the midbrain and end in part in the gray matter of 

 the inferior colliculus, of the median or internal geniculate, and, 

 according to Van Gehuchten, in a small mass of nerve cells in the 

 midbrain known as the superior nucleus of the fillet. From this 

 second or third termination another set of fibers, the auditory 

 radiation, continues forward through the posterior extremity of 

 the internal capsule to end in the superior temporal gyrus (see 

 Fig. 76, E). According to Flechsig,* who has studied the course 

 of these fibers in the embryo by the myelinization method, the 

 main group passes from the internal geniculates to the transverse 

 gyri of the temporal lobe within the fissure of Sylvius. The in- 

 ternal geniculates, in man at least, have therefore the function 

 of a subordinate auditory center, as the external geniculates have 

 the function of a subordinate visual center. The internal genic- 

 ulates 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 posterior 

 margin of the chiasma. The auditory path, therefore, involves 

 the following structures: The spiral ganglion, the cochlear nerve, 

 accessory nucleus and tuberculum acusticum, corpus trapezoideum, 

 medullary striae, superior olivary, lateral fillet, inferior colliculus, 

 median geniculate, Gudden's commissure, auditory radiation, and 

 temporal cortex. 



The Motor Responses from the Auditory Cortex. Accord- 

 ing to Ferrier, stimulation of the cortex of the temporal lobe (infe- 

 rior convolution) causes definite movements, such as pricking of 

 * Flechsig, " Localisation der geistigen Vorgiinge," Leipzig, 1896. 



