THE CEREBRAL NERVES 



361 



the facial nerve arise from the cells of the geniculate ganglion, which are in turn 

 derived from the ganglion crest (Streeter). This ganglion is present at the third 

 week (Fig. 341), located cranial to the acoustic ganglion. The centrally directed 

 processes of the geniculate ganglion enter the alar plate and form part of the 

 solitary tract. The peripheral fibers in part course with motor fibers in the chorda 

 tympani, join the mandibular branch of the trigeminal nerve and end in the sense 

 organs of the tongue. Other sensory fibers form later the great superficial petrosal 

 nerve, which extends to the spheno-palatine ganglion. 



The motor fibers of the facialis at first course straight laterally passing 



Nucl. n. hypoglOSS 



N. aeceasorlua 



Funic 

 posterior 



Fig. 345. — Reconstruction of the nuclei of origin and termination of the cerebral nerves in an embryo 

 of 10 mm. The somatic motor nuclei are colored red (Streeter). X 30. 



cranial to the nucleus of the abducens. The nuclei of the two nerves later 

 gradually shift their positions, that of the facial nerve moving caudally and 

 lateralwards, while the nucleus of the abducens shifts cranialwards. As a result, 

 the motor root of the facial nerve in the adult bends around the nucleus of the 

 abducens producing the genu or knee of the former. The two together produce 

 the rounded eminence in the floor of the fourth ventricle known as the facial collic- 

 ulus. 



9. The Glossopharyngeal Nerve takes its superficial origin just caudal to the 

 otic vesicle (Figs. 340, 344 and 346). Its few motor fibers arise from neuroblasts 

 in the basal plate beneath the fifth neuromeric groove. These neuroblasts form 



