SENSE AREAS AND ASSOCIATION AREAS. 201 



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 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 nu~ 

 cleus 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 coch- 

 lear 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 an- 

 other 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. 77, E). According to Flechsig,* who has 

 studied the course of these fibers in the embryo by the myeliniza- 

 tion method, the main group passes from the internal geniculates to 

 the transverse gyri of the temporal lobe within the fissure of Sylvius. 

 The internal geniculates, in man at least, have therefore the func- 

 tion of a subordinate auditory center, as the external geniculates 

 have the function of a subordinate visual center. The internal 

 geniculates are connected with the inferior colliculus, and also, it 

 will be remembered, with each other, by commissural fibers (Gud- 

 den'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 Physiological Significance of the Lower Auditory Cen- 

 ters. The auditory path connects directly with two or three sets 

 of nerve cells before terminating finally in the cortex. The lower 

 centers in pons, midbrain, or thalamencephalon connect probably 

 with motor paths through which co-ordinated reflex movements 

 may be effected. But whether or not any perceptible degree of con- 

 sciousness can be mediated through these lower centers remains 

 undetermined. Goltz's dog without its cerebrum could be awak- 

 ened from sleep by loud noises, and Schafer contends that in 

 monkeys the removal of both temporal lobes is not followed by 

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



