VERTEBRA TA. 



415 



envelops the three pairs of vertebrate sense-organs. The 

 notochord runs in the ventral wall of this membranous 

 cranium as far as the mid-brain, terminating behind the 

 infundibulum (Fig. 293, page 407). The first cartilages 



Fig. 299. — Development of Vertebrate Cranium. 



Dorsal View of Embryo. 



Trabeculae. 



Parachordals. 



Notochord. 



Auditory Sac. 



Fig. 300. — Development of Vertebrate Cranium. 



(Later stage.) 



Pituitary Fossa.. 



Basis Cranii. 



Nasal Capsule. 



to appear are two pairs of plates alongside of the noto- 

 chord. The first pair extends forwards on either side 

 of the infundibulum as the traheculce^ the hinder pair, 



