CENTRAL NERVOUS SYSTEM. 237 



goes to the inner car. The cochlear portion of the inner car mediates sensa- 

 tions of sound and is connected with the bulb by means of the aervus coch- 

 leae; the cochlear branch of the eighth nerve. The cell-bodies of the aervus 

 cochlea? are located in the spiral ganglion of the cochleae, which is homologous 

 with the dorsal root ganglion of a spinal nerve. The ganglion cells are 

 bipolar or diaxonic, one axonc passing toward the organ of Corti in the 

 cochlea, and the other toward the bulb. 



On reaching the bulb, the nerve formed by the latter axones enters in a 

 large measure the nucleus nervi cochlea? ventralis, 1 and to a less extent the 

 nucleus nervi cochlea? dorsalis. According to Held." some of the root-fibres 

 entering the ventral nucleus may be continuous as far as the superior quad- 

 rigemina, reaching that level by way of the trapezoid e um, the superior olive, 

 the lateral lemniscus, and the colliculus inferior; to all of which gray masses, 

 including the nucleus nervi cochlea? dorsalis, these axones may give collat- 

 erals. Further, some fibres may terminate in any of the localities reached 

 by the collaterals. Besides the direct continuations of the afferent axones by 

 way of the ventral nucleus, each one of the localities mentioned above, includ- 

 ing both the dorsal and ventral cochlear nuclei, contains cell-bodies forming, 

 on the one hand, nuclei of termination, and on the other by their axones con- 

 tinuing the auditory pathway even to the cerebral cortex (Held). A group 

 of central cells with their bodies in the nucleus nervi cochlea? dorsalis send 

 their axones across the floor of the fourth ventricle, forming the stria? acustica?. 

 These axones in part decussate with the corresponding fibres — the crossing 

 occurring in the raphe — and then either as direct or crossed fibres find their 

 way cephalad by the same path (with some additions) as that described in 

 connection with the ventral nucleus. 



B. Vestibular Root. — Quite separate from the cochlear is the vestibular 

 division of the eighth nerve, and this separateness is a strong argument against 

 the suggestion sometimes made that the portions of the labyrinth innervated 

 by the vestibular nerve, may also mediate sensations of sound. The besf 

 evidence shows the nerve to convey those impulses from the macula acustica 

 utriculi and the crista' ampullares, which are largely utilized in the mainten- 

 ance of the equilibrium and in arousing the sensations of the movement of 

 the body as a whole. The peripheral neurones which give rise to the vestib- 

 ular fibres have their cell-bodies collected in the vestibular ganglion. The 

 peripheral axones of the ganglion-cells end among sensory epithelium of the 

 parts just named, while the central axones, forming a larger rool than that 

 associated with the cochlea, join the bulb at the caudal (■d^c of the puns, the 

 vestibular root lying to the cephalic side of the cochlear root. Having 

 entered the bulb, the axones divide, after the manner of dorsal root fibres, 

 into an ascending and a descending branch, which find their nuclei of termina- 

 tion in :i (1) the nucleus nervi vestibuli spinalis (the radix descendens); ('_') in 



1 Barker: The Nervous System "nil its Constituent X* "nun*, 189'.*, pp. "ill 555. 



2 Held : Arehivfur Physiologie, Aunt. Abth., Leipzig, L893. 



3 Barker: '/'//< Nervous System mid Us Conxliiurnt \i-iirmim, 1899, p. <>_!7. >i .«</. 



