VIII.] THE FRONTO-NASAL PROCESS. 



FIG. 80. 



247 



A. HEAD OF EMBRYO CHICK OF THE FOURTH DAY VIEWED FROM 



BELOW AS AN OPAQUE OBJECT. (Chromic acid preparation.) 



C.ff. cerebral hemispheres. FB. vesicle of the third ventricle. 

 Op. eyeball, nf. naso-frontal process. M. cavity of mouth. 

 S.M. superior maxillary process of F. 1, the first visceral 

 fold (mandibular arch). F. 2, F. 3, second and third 

 visceral folds. N. nasal pit. 



In order to gain the view here given the neck was cut across 

 between the third and fourth visceral folds. In the section e 

 thus made, are seen the alimentary canal al with its collapsed 

 walls, the neural canal ra.c., the notochord ch., the dorsal aorta 

 AO.j and the jugular veins V. 



B. The same seen sideways, to shew the visceral folds. 

 Letters as before. 



After a while the outer angles of the fronto-nasal 

 process, enclosing the expanded termination of the 

 trabeculae, project somewhat outwards on each side, 

 giving the end of the process a rather bilobed appear- 

 ance. These projecting portions of the fronto-nasal pro- 

 cess form on each side the inner margins of the rapidly 



