806 



THE NERVOUS SYSTEM 



inferior nucleus (nucleus spinalis). The latter is a downward prolongation of the 

 general nucleus vestibularis which accompanies the descending root of the nerve. 



From the cells of the lateral and inferior nuclei axones are given off which form 

 reflex paths to the lateral column of the spinal cord (vestibulo-spinal fasciculus, 

 fig. 571). From both the lateral nucleus and the superior nucleus a special path is 

 given off which passes upwards and terminates in the nucleus fastigii (cerebelli) of 

 the opposite side and in the nucleus dentatus and the cortex of the vermis. Also, 

 fibres arising in the nuclei fastigii are said to terminate in the lateral (J)eiters') nucleus 

 in addition to those which descend into the ventral marginal fasciculus of the spinal 

 cord. From the medial and also from the superior nucleus fibres pass to the medial 

 longitudinal fasciculus of both sides, and are distributed to the nucleus of the abducens 

 of the same side and to the nuclei of the trochlear and oculomotor nerves and of the 

 motor portion of the trigeminus of the same and opposite sides. Other fibres arising 

 in the vestibular nucleus ascend to the lateral portion of the thalamus. 



.Many of the anatomical details of the central connections of the vestibular nerve 

 have not yet been determined with exactness. In addition to whatever other func- 

 tions it may have, it is considered to be the nerve of equilibration, and the connec- 



FIG. GOO. TRANSVERSE SECTION OF MEDULLA AT INFERIOR BORDER OF PONS. 



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PYRAMID 

 NUCLEUS ARCUATUS 



tions noted above may be considered the pathways by which it exercises this function. 

 The fibres of the apparatus which are represented in the spinal cord are supposed to 

 convey impulses to the ventral horn (motor) cells of the cord as far down as the lum- 

 bar region. 



(2) The cochlear nerve, probably the auditory nerve proper, arises as the central 

 processes of the bipolar cells of the spiral ganglion of the cochlea. In the lateral 

 periphery of the restiform body, just as it enters the pons. the nerve finds its two 

 nuclei of termination, the ventral nucleus and the dorsal nucleus (tuberculum acusti- 

 cum, fig. 591). 



From the dorsal nucleus arise the striae medullares acustici. These bundles, more 

 or less inconstant in man, pass around the dorsal aspect of the restiform body and 

 course just under the ependyma of the floor of the fourth ventricle to the mid-line, 

 where they suddenly turn downwards into the substance of the medulla, and in doing 

 so, cross to the opposite side and join the lemniscus. As the lemniscus becomes 

 separated higher up into a medial and lateral portion, these fibres course in the lateral 

 lemniscus and are distributed chiefly to the grey substance of the inferior quadri- 

 geminate body of that side. 



From the ventral nucleus of termination fibres arise which terminate about the 



