EELATIONS OF THE CRAXIAL XERYES. 



ni 



fifth pair or trip-eminus, the facial, the g-losso-pharyngeal, and the 

 l^neumo-gastric. The two first are situated iu front, and the two latter 

 behind the auditory sac. These nerves all divide or fork above a 

 visceral cleft, one division going to the posterior face of the arch in 

 front of the cleft, the other to the anterior face of the arch behind it. 



540. 





Fig. 540. — Embryo of tue Ciiioii at tub end of the Fouhth Day (from Foster and 



Bcalfour). 



The amnion has been removed ; Al, allantois ; Clf, cerebral hemispheres ; FS, 

 thalamencephalon, with Pn, the pineal gland projecting from its summit; MB, mid- 

 brain ; Cb, cerebellum ; IV, V, fourth ventricle ; Z, lens ; chs, choroid slit ; C'en V, 

 iiuditory vesicle ; sm, superior maxillary process ; IF, 2F, &c., first, second, third and. 

 fourth visceral folds ; V, fifth nerve in two divisions, one to the eye, and the other to 

 the first visceral arch ; VII, seventh nerve passing to the second visceral arch ; Gph, 

 glosso-pharjmgeal nerve passing to the third visceral arch ; Pg, pneumo -gastric nerve 

 passing to the fourth arch ; / V, investing mass ; ch, notochord ; Mt, the heart ; HIP, 

 muscle plates ; W, wing ; HL, hind limb. 



The orbito-nasal and the palatine divisions of the trigeminus belong 

 to the trabecular arch, the former above, the latter below the optic 

 nerve. Of the other division, one part (the superior maxillary nerve) 

 follows the palato-pterygoid arch, the other (inferior maxillary nerve) 

 accompanies tlie mandibular arch. 



The facial nerve (portio dura of seventh pair) divides above the 

 tympano-eustachian passage, its anterior part (chorda tympani) going 

 to the posterior side of the mandibular arch, and its posterior part 

 (descending branch of facial) to the outer or anterior side of the hyoid 

 arch. 



The glosso-pharyngeal nerve, by a similar division, goes by its inner 

 or anterior branch (lingual) to the inner or posterior side of the hyoid 

 arch, and by its other division (pharyngeal) to the front of the first 

 branchial or thyro-hyoid arch. 



