THE CEREBRAL NERVES 



363 



cells of the geniculate ganglion, which are in turn derived from the ganglion 

 crest (Streeter). This ganglion is present in 7 mm. embryos (Fig. 358), 

 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 laterad, passing 

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



Nucl. motor. n,X (amblguui) 



Nud. n. hypogloMl 



N. csoriu v-- 



FIG. 364. 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. 



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

 laterad, while the nucleus of the abducens shifts cephalad. 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 colliculus. 



9. The Glossopharyngeal Nerve takes its superficial origin just caudal 

 to the otic vesicle (Figs. 358, 363 and 365). Its few motor fibers arise 

 from neuroblasts in the basal plate beneath the fifth neuromeric groove. 

 These neuroblasts form part of the nucleus ambiguus, a nucleus of origin 

 which the glossopharyngeal shares with the vagus (Fig. 364). The motor 



