AREAS OF THE MEDULLA OBLONGATA 883 



pass across the raphe to the contralateral interolivary stratum to join the medial 

 lemniscus, establishing connections with the thalamus and cortex; other axones 

 join the tractus nucleocerebellaris. 



2. Efferent Portions. The efferent components of the vagus and glossopharyn- 

 geal nerves come from two sources (a) the dorsal efferent (vagal) nucleus and 

 (&) the nucleus ambiguus. 



The dorsal efferent nucleus lies ventromesad of the principal nucleus, alae cinereae 

 and laterad of the hypoglossal nucleus. The axones from its cells pass obliquely 

 ventrolaterad to enter the root fascicles of the vagus and to become distributed to 

 the oesophagus, stomach, trachea, and bronchi. Whether the glossopharyngeal 

 nerve receives efferent axones or not is still in debate. 



The nucleus ambiguus (nidus pharyngei so termed in contradistinction to the 

 nidus laryngei) is a rod-like mass of large, multipolar cells seen, in trans-sections, 

 lying in the gray, reticular formation midway between olive and fasciculus soli- 

 tarius and apparently a cephalic continuation of the accessory nerve nucleus. 

 The axones arising from its cells run dorsimesad at first, then turn abruptly ectad 

 to join the vagus (and glossopharyngeal?) nerve-root fascicles, becoming dis- 

 tributed to the pharyngeal muscles, oesophagus, Cricothyroid, and the other 

 Laryngeal muscles. 



The Acoustic Nerve Nuclei. The acoustic nerve consists of a cochlear and a 

 vestibular division; the former is concerned with the sense of hearing, the latter 

 with the sense of equilibrium. 



1. The cochlear or true auditory nerve arises in the bipolar cells of the cochlear 

 spiral ganglion; its axones terminate in (a) the dorsal nucleus (tuberculum acusti- 

 cuni), a pyriform mass on the dorsolateral aspect of the restiform body, and (6) 

 the ventral nucleus, somewhat detached from the former. 



From the dorsal nucleus cells arise the axones which compose the striae acusticae, 

 myelinic fibre bundles traversing the ventricular surface to near the median 

 sulcus, dipping into the tegmental substance, crossing to the opposite side in the 

 raphe, and eventually joining the lateral lemniscus to end in the posterior quadri- 

 geminal body and internal geniculate body. 



From the ventral nucleus cells arise the axones which course transversely to form 

 the trapezium at the contact zone of the pons proper and tegmentum. Additional 

 axones from cells in the superior olives of both sides and in the trapezium itself 

 increase the bulk of this tract; some of the primary axones end in relation with 

 these cells. These axone groups form the contralateral lemniscus lateralis, which 

 contains the intercalated nucleus of the lateral lemniscus as a relay station, to be 

 continued to the posterior quadrigeminal and to the internal geniculate bodies 

 and thence to the cortical auditory "centre" in the supertemporal gyre. 



2. The vestibular nerve axones arise in the bipolar vestibular ganglion cells 

 ((T. of Scarpa), enter the brain stem, and bifurcate into ascending and descending 

 rami, which terminate as follows: The ascending rami end in the medial nucleus 

 (Schwalbe's) ; the descending rami end in the spinal vestibular nucleus, which 

 extends down to the gracile and cuneate nuclear level; another group of axones 

 ends in the lateral nucleus (nucleus magnocellularis) (Deiters'); while a fourth 

 and last group ends in the superior nucleus (Bechterew's). From the cells of all 

 these nuclei of termination axones proceed toward the cortex, dentate nucleus, 

 and nucleus fastigii of the cerebellum, as part of the nucleocerebellar tract, to the 

 nuclei of the abducent, trochlear, trigeminal, and oculomotor nerves by collaterals 

 from axones in the medial longitudinal bundle, to the thalamus, and to the ventral 

 horn nuclei of the spinal cord along the tractus vestibulospinalis. The far- 

 reaching and complex connections of the vestibular nerve with the cerebellum and 

 the centres for eye muscles and the spinal centres for bodily movements make this 

 cranial nerve a most interesting subject for the active research now going on. 



