860 



NEUROLOGY 





fibers join the optic tract as it passes over the edge of the medial geniculate ard 

 passes through the posterior part of the optic chiasma. It is probably a commissure 

 connected with the auditory system. 



The Vestibular Nerve (vestibular root, VIII cranial) arise from the bipolar cells 

 in the vestibular ganglion (Scarpa's ganglion). The peripheral fibers end in the 

 semicircular canals, the saccule and the utricle, the end-organs concerned with 

 mechanism for the maintenance of bodily equilibrium. The central fibers enter 

 the medulla oblongata and pass between the inferior peduncle and the spinal tract 

 of the trigeminal. They bifurcate into ascending and descending branches as do 

 the dorsal root fibers of all the spinal nerves and all aft'erent cranial nerves. The 

 descending branches terminate in the dorsal (medial) vestibular nucleus, the 

 principal nucleus of the vestibular nerve. This nucleus is prolonged downward 

 into a descending portion in which end terminals and collaterals of the descending 

 branch. The ascending branches pass to Deiters's nucleus, to Bechterew's nucleus 



and through the inferior peduncle 



6 



5 



18.. 



5... 



of the cerebellum to the nucleus 

 tecti of the opposite side. 



The dorsal vestibular nucleus 

 (medial or principal nucleus) is a 

 large mass of small cells in the 

 floor of the fourth ventricle under 

 the area acustica, located partly 

 in the medulla and partly in the 

 pons. The striae medullares cross 

 the upper part of it. It is sepa- 

 rated from the median plane by 

 the nucleus intercalatus. Itsaxons 

 pass into the posterior longitudi- 

 nal bundle of the same and the 

 opposite side and ascend to ter- 

 minate in the nucleus abducens 

 of the same side and in the troch- 

 lear nucleus and the oculo-motor 

 nucleus of the opposite side, and 

 to the motor nuclei of the trigem- 

 inal on both sides. The descending 

 portion, the nucleus of the descend- 

 ing tract extends downward as far as the upper end of the nucleus gracilis, and the 

 decussation of the medial lemniscus. It is sometimes called the inferior vestibular 

 nucleus. Many of its axons cross the midline and probably ascend with the medial 

 lemniscus to the ventro-lateral region of the thalamus. 



The lateral vestibular nucleus (Deiters's nucleus) is the continuation upward and 

 lateralward of the principal nucleus, and in it terminate many of the ascending 

 branches of the vestibular nerve. It consists of very large multipolar cells whose 

 axons form an important part of the posterior longitudinal bundle of the same and 

 the opposite sids. The axons bifurcate as they enter the posterior longitudinal 

 bundle, the ascending branches send terminals and collaterals to the motor nuclei 

 of the abducens, trochlear and oculomotor nerves, and are concerned in coordinating 

 the movements of the eyes with alterations in the position of the head ; the descending 

 branches pass down in the posterior longitudinal bundle into the anterior funiculus 

 of the spinal cord as the vestibulospinal fasciculus (anterior marginal bundle) and 

 are distributed to motor nuclei of the anterior column by terminals and collaterals. 

 Other fibers are said to pass directly to the vestibulospinal fasciculus without 

 passing into the posterior longitudinal bundle. The fibers which pass into the 



FIG. 761. Terminal nuclei of the vestibular nerve, with their 

 upper connections. (Schematic.) 1. Cochlear nerve, with its 

 two nuclei. 2. Accessory nucleus. 3. Tuberculum acusticum. 

 4. Vestibular nerve. 5. Internal nucleus. 6. Nucleus of Deitera. 

 7. Nucleus of Bechterew. 8. Inferior or descending root of 

 acoustic. 9. Ascending cerebellar fibers. 10. Fibers going to 

 raph6. 11. Fibers taking an oblique course. 12. Lemniscus. 13. 

 Inferior sensory root of trigeminal. 14. Cerebrospinal fasciculus. 

 15. Raph6. 16. Fourth ventricle. 17. Inferior peduncle. Origin 

 of strhe medullares. (Testut.) 



