THE DEEP CONNEXIONS OF THE CEEEBKAL NEEVES. 599 



ind submaxillary ganglia (as their white rami comraunicantes), and are largely 

 3oncerned with the regulation of the secretory activity of the large salivary glands 

 ind other glands around the mouth. 



The facial nucleus is situated close to the place where the nerve emerges from 

 the brain, but the nerve does not at once pass to this point of exit. It pursues 

 a long and devious path within the pons before it finally reaches the surface. 

 This intrapontine part of the nerve may be divided into three parts, viz. : (1) a 

 radicular part, (2) an ascending portion, and (3) an emergent part. 



The radicular part of the facial nerve (Fig. 531) is composed of a large number 

 of fine, loosely arranged bundles of fibres, which issue from the lateral and dorsal 

 aspect of the nucleus and proceed backwards and slightly medially through the 

 pons. Beaching the floor of the fourth ventricle they curve medially, and the 

 bundles which He highest up sweep over the lateral and dorsal aspect of the 

 inferior part of the nucleus of the sixth nerve. Close to the median plane they 

 (turn sharply upwards and are collected into a single solid nerve-bundle, which 

 constitutes the ascending part of the facial nerve (Figs. 530 and 531). This 

 proceeds upwards immediately beneath the ependyma of the ventricular floor 

 on the dorsal aspect of the medial longitudinal bundle, and along the medial side 

 of the abducent nucleus for a distance of about five millimetres. Then the 

 nerve bends laterally at a right 

 angle, and curves a second time 

 over the dorsal aspect of the ab- 

 ducent nucleus. This gives rise 

 to a prominent hemispheral pro- 

 jection in the floor of the fourth 

 ventricle, the colliculus facialis (Fig. 

 531 and Fig. 482, p. 550). The 

 nerve now passes straight to the 

 place of exit from the brain, and 

 this part of the intrapontine trunk 

 may be termed the emergent por- 

 tion (Figs. 498 and 531). The 

 facial nerve thug forms a curved 

 loop over the dorsal aspect of the 

 abducent nucleus. The emergent 

 part of the nerve takes an oblique 

 course through the pons to reach 

 the surface. It inclines laterally 

 s and downwards as it proceeds to- 

 wards the ventral aspect of the pons, 

 and on its way it passes between 

 its own nucleus and the tract us 

 spinalis of the trigeminal nerve. 



Entering the facial nucleus, 

 | and ending in fine terminal arborisa- 

 1 tions around its cells, are many 

 fibres from the opposite pyramidal 

 tract ; fibres from the spinal tract 

 1 of the fifth nerve ; fibres from the 

 corpus trapezoideum, etc. The nucleus is thus brought into connexion with the 

 motor area of the cerebral cortex, with the trigeminal nerve or sensory nerve of 

 the face, and with the acoustic nerve. 



The peculiar course of the efferent fibres of the facial nerve within the pons 

 is to be explained in accordance with the general principle regulating migrations 

 of nerve-cells, to which reference has already been made (p. 554). In the embryo 

 the nucleus facialis develops alongside the nucleus abducens. The latter, con- 

 trolling one of the eye-muscles, receives most of its afferent impulses from the 

 medial longitudinal bundle (descending from the optic centres in the superior 

 colliculus), and therefore it remains alongside the medial longitudinal bundle 



39 & 



FIG. 531. DIAGRAM OF THE INTRAPONTINE COURSE OF 

 THE FACIAL NERVE. 



Sub. gel. rol. refers to the nucleus of the spinal trigeminal 

 tract. 



