VI.] 



THE CRANIAL NERVES. 



FIG. 42. 



127 



HEAD OF AN EMBRYO CHICK OF THE THIRD DAY (SEVENTY- 

 FIVE HOURS) VIEWED SIDEWAYS AS A TRANSPARENT OBJECT. 



(From Huxley.) 



la. cerebral hemispheres. Ib. vesicle of the third ventricle. II. 

 mid-brain. III. hind-brain, g. nasal pit. a. optic vesicle. 

 6. otic vesicle, d. infundibulum. e. pineal body. h. noto- 

 chord. V. fifth nerve. VII. seventh nerve. VIII. united 

 glossopharyngeal and pneumogastric nerves. I, 2, 3, 4, 5 

 the five visceral folds. 



branch of the fifth nerve) is distributed to the first 

 visceral arch. 



The second mass (Figs. 42 and 67, VII) is the rudi- 

 ment of the seventh, or facial nerve, and of the audi- 

 tory nerve. It is the nerve of the second visceral arch. 



The two masses behind the auditory vesicle repre- 

 sent the glossopharyngeal and pneumogastric nerves 

 (Fig. 42, VIII, Fig. 67, G. Ph. and Pg). At first 

 united, they subsequently become separate. The glosso- 

 pharyngeal supplies the third arch, and the pneumo- 

 gastric the fourth and succeeding arches. 



The later development of the cranial nerves has only been 

 partially worked out, and we will confine ourselves here to a very 



