282 THE RHOMBENCEPHALON, 



motor nucleus is close to the median plane and is separated from 

 the ependyma of the ventricular floor only by the fibers of the 

 seventh or facial nerve. It is situated in the colliculus facialis 

 (Figs. 86 and 88). . The root-fibers of the facial nerve run lateral 

 to the sixth nucleus, describe a loop on its dorsal surface and then 

 return lateral to it. Cortical Connection. The abducent nucleus 

 receives the end-tufts of motor fibers from the opposite pyramidal 

 tract and from the cerebro-pontal tracts. It receives reflex 

 impulses through the anterior and medial longitudinal bundles 

 and the pedicle of the superior olivary nucleus ; and perhaps, also, 

 through the brachium conjunctivum from the cerebellum. The 

 axones of the cell-bodies in the adbucent nucleus run in two direc- 

 tions: The greater number run ventro-lateralward and emerge 

 at the lower part of the pons, as abducent nerve; a small bundle 

 of axones runs to the oculomotor nucleus on the opposite side 

 by way of the medial longitudinal bundle. The former inner- 

 vates the external rectus muscle of the eye on the same side as the 

 nucleus ; the latter, through the third nerve, innervates the internal 

 rectus of the opposite eye, though that muscle receives independent 

 fibers from the third, also. 



The nucleus of the facial or seventh nerve (n. nervi facialis) 

 is genetic or motor (Fig. 88). It is situated deep in the pons, in 

 the lateral part of the formatio reticularis, beneath the superior 

 fovea. Immediately ventral to it is the superior olivary nucleus, 

 and the substantia gelatinosa (Rolandi) lies dorso-lateral to it. 

 The nucleus is placed midway between the spinal tract of the 

 fifth nerve and the olivary fasciculus. Cortical Connections. 

 It receives voluntary motor impulses from the cerebral cortex 

 of the opposite hemisphere via the pyramidal tract; and, prob- 

 ably, fibers of the cerebro-pontal tracts terminate in it. These 

 establish its motor connections. The reflex, connections of the 

 facial nucleus are established by fibers from the spinal tract of the 

 trigeminal nerve, from the trapezoid body (Cunningham), and 

 from the medial longitudinal bundle. The axones of the cell- 

 bodies in the nucleus facialis all enter the root of the facial nerve. 

 By its direction this root is divided into three parts, viz., two 

 distinct parallel parts, joined by a very short ascending portion. 



