506 



THE ORGANS 



ventr /y 



m!i 



and face. The dorsal group (to superior branch of facial) innervates the frontalis, 

 corrugator supercilii and orbicularis palpebrarum Among the terminals in the 

 nucleus have been distinguished collaterals (reflex) from the lateral part of the 

 reticular formation, from the secondary acoustic and trigeminal tracts and other 

 adjacent fibres; also terminals of the coUiculo-spinal tract. Whether the nucleus 

 receives direct terminals from the pyramids or whether fibres of the latter 

 are only connected with it via intercalated neurones is uncertain. 



Some of the root fibres of the VI 

 are usually seen in the ventral border 

 of the tegmentum. For nucleus see 

 next section. 



Afferent Roots, their Terminal 

 Nuclei and Secondary Tracts. — The 

 afferent vestibular root fibres enter at 

 the caudal border of the pons and pass 

 lateral to the spinal V, mesial to the 

 ventral cochlear nucleus and restiform 

 body, and enter the field previously 

 occupied by the descending vestibular 

 root, the fibres of which are a continua- 

 tion of the root. Scattered large cells 

 in this region form the nucleus of 

 Deiters. Dorso-mesial to this is still 

 the medial vestibular terminal nucleus 

 and dorsal to Deiters' at the external 

 angle of the fourth ventricle is the 

 superior vestibular terminal nucleus (von 

 Bechterew). Fibres seen passing from 

 the vestibular region to the cerebellum 

 and lying near the ventricle are partly 

 vestibular root fibres to the cerebellum 

 (especially to the nucleus tecti, or 

 fastigii, see below), and partly descend- 

 ing fibres from cerebellar nuclei 

 (especially from the nuclei fastigii, forming jastigio-bulbar fibres) to Deiters' 

 nucleus, other vestibular nuclei, and other cells in the reticular formation. It 

 is thus evident that such nuclei as Deiters' may act as parts of vestibular - 

 bulbo-spinal reflex arcs and also as parts of eft'erent and possibly afferent 

 cerebellar paths. Internal arcuate fibres from the vestibular area are probably 

 principally fibres (secondary tracts) from the various vestibular nuclei to the 

 medial longitudinal fasciculus and other tracts in the reticular formation. 

 (Comp. pp. 499, 507, 513, Figs. 339, 345.) 



The nucleus olivaris superior lies ventral to the nucleus facialis and lateral 

 to the central tegmental tract. This nucleus together with several other small 

 nuclei in its immediate vicinit}^ (preolivary nucleus, semilunar nucleus, trapezoid 

 nucleus) is one of the nuclei intercalated in the cochlear path (Fig. 338) which 

 provides reflex connections {e.g., with the \1 and \TI motor nuclei). Lateral 



/'/•'■ 



Fig. 341. — Diagram of Origin of Sixth 

 and Seventh Cranial Nerves. (Schafer.) 

 pyr, Pyramid; or, restiform body; dV, 

 spinal root of fifth nerve; Vcntr. IV, fourth 

 ventricle; VIII .v, vestibular root of eighth 

 nerve; n.VI, chief nucleus of sixth nerve; 

 n'VI , accessory nucleus of sixth nerve; VI, 

 sixth nerve; n.VII, nucleus of seventh 

 nerve, from which the axones pass dorso- 

 mesially to the floor of the ventricle, where 

 the}- turn brainward, appearing as a bundle 

 of transversely cut fibres, a VII, and ascend 

 to the "genu," g, where they turn and pass 

 ventro-laterally and somewhat caudally to 

 the surface as the seventh nerve, VII. 



