THE GREAT AFFERENT SYSTEMS 



309 



The Neural Mechanism for Hearing. The spiral organ of Corti within the 

 cochlea is connected with the auditory center in the cerebral cortex by a chain 

 of three or more units. 



Neuron I. The bipolar cells of the spiral ganglion within the cochlea send 

 each a peripheral process to end in the spiral organ of Corti. Each sends a central 

 branch to ramify in the cochlear nuclei, where it forms sy nap tic connections 

 with the auditory neurons of the second order (Fig. 233). 



Transverse temporal gyrus 



Auditory radiation 



Medial genicnlate body 

 Inferior cotticulus 



v Lateral lemnisci 



Collaterals to nucleus of 

 lateral lemniscus 



/Strife medullares 



,-Dorsal cochlear nucleus 



-Ventral cochlear nucleus 

 Cochlear nerve 

 r Vestibular nerve 



Rostral portion of the pons-/- ( 



!~\ 



J ! 

 Caudal portion of the pons-\^ 



Superior olive '' 



Trapezoid body ' 



Nucleus of the trapezoid body 



Fig. 233. Diagram of the auditory pathway. (Based on the researches of Cajal and Kreidl.) 



Neuron II. The cells located in the ventral and dorsal cochlear nuclei give 

 rise to fibers, which after crossing the median plane form the lateral lemniscus 

 of the opposite side. Those from the ventral cochlear nucleus cross the pons in 

 the trapezoid body, giving off collaterals to the superior olivary nuclei and the 

 nuclei of the corpus trapezoideum, and may be joined by fibers taking origin in 

 these nuclei. Lateral to the contralateral superior olivary nucleus they turn 

 abruptly rostrad in the lateral lemniscus. The fibers from the dorsal cochlear 

 nucleus run in the striae medullares of the fourth ventricle, and then, dipping 



