THE NERVOUS SYSTEM 501 



EXPLANATION OF FIG. 338 



Fig. 338. — Diagram showing Connections of the Cochlear Portion of the Auditory 

 (VIII) Nerve. A, Section at level of superior colliculi (Attt. corp. quad.) and red 

 nucleus; B, through level of inferior colliculi {Corpus, quad. ^05^); C, through level of 

 nucleus of lateral lemniscus {Nu. lent, lal.); D, through pons at level of VIII nerve. 

 Spacing between the ditYerent levels is not proportionate. In B and C the basis 

 pedunculi is omitted. Each neurone group is indicated by one or several individual 

 neurones. 



Neurone No. i. — Cell bodies in spiral ganglion (gang, spiralis); peripheral processes 

 end in organ of Corti; central processes terminate principally in ventral or accessory 

 nucleus {N'u. accessorius) and lateral nucleus {A^u. lateralis) or tubcrculum acusticum; 

 some also terminate in superior olives {Oliva superior), and nuclei of trapezoid body {Nu. 

 Corp. trapezoidei) of same and opposite sides. 



Neurone jYo. 2. (and 3 ?).• — rAxones of cells in accessory nucleus, in superior olives, and 

 in nuclei of trapezoid body, constitute a ventral path in the lower border of the tegmen- 

 tum, and form the lateral part of the lateral lemniscus {Lemniscus laleralis) or lateral 

 fillet on the opposite side. Axones of cells in the lateral nucleus trav'erse the floor of the 

 fourth ventricle as the striae meduUares, forming a dorsal pathway, decussate and then 

 turn ventrally to a point dorsal to the superior olive and join the lateral lemniscus as its 

 mesial part. Some axones also of cells in the accessory and lateral nuclei pass dorsally, 

 looping around the restiform bod}', and then proceed ventrally (bundle of Held) to join 

 the opposite lemniscus. The lateral lemniscus passes upward to the inferior colliculus, 

 some of the axones terminating en route in the nucleus of the lateral lemniscus. From 

 cells in this nucleus some axones again join the lateral lemniscus, and a few decussate and 

 then pass upward to the inferior coUiculius. The axones of the lateral lemniscus ter- 

 minate in the inferior colliculus, or pass on to terminate in the internal geniculate 

 body, merely giving off collaterals to the superior colliculus. Some fibres of the lateral 

 lemniscus probably go to the superior colliculus. 



Neurone No. 3 (and 4?). — Axones of cells in the gray matter of the inferior col- 

 liculus form its brachium {Brachium corp. quad, post.) and ascend to terminate in the 

 internal or medial geniculate body {Corp. genie, inter.). 



Neurone iVo. 4(and 5?). — Axones of cells in the internal geniculate body pass as a 

 part of the thalamic radiation 'cia the posterior part of the internal capsule to the cortex 

 of the temporal lobe of the cerebrum. 



The axones which constitute the ventral path (Neurones i and 2) form a bundle of 

 fibres known as the trapezoid bod}' {Corpus trapezoideuin) or trapezius. The decussa- 

 tion of these is peculiar in that the dorsal axones of the bundle on one side become the 

 ventral ones on the opposite side; this accounts for the convergence of the axones at the 

 median raphe. 



Axones of cells in the superior olive pass to the nucleus of VI nerve (reflex). There is 

 possibly also a descending path from the lateral nucleus to the spinal cord (not 

 indicated). 



