CONARTO-HYPOPHYSIAL TRACT. 



the direction of that region of the brain which, at a later 

 period, is occupied hy the conario-hypophysial relics is 

 described and figured, under the term " aditus anterior " and 

 " pharynx primitif " *. 



In fig. 5 Embryon du poulet de 44 heures a l is 

 the anterior or first ("premiere") cerebral vesicle; d 2, the 

 second cerebral vesicle; c, the notochord ; d, ''primitive 

 pharynx." 



The branchial chamber, e, with the pulsating vesicle and 

 first rudiments of gills, here repeat the branchial sac which 



receives the oral aperture of the alimentary canal in the 

 Ascidians, a structure which is the condition of the deviation, 

 in a higher step of the Life Series, of the oesophagus from its 

 primary course, and of its communication with the precocious 

 gill-chamber, which then becomes the vertebrate mouth, 

 retaining the closer resemblance to the Ascidian branchial sac 

 in the lowest (piscine) forms of Vertebrata {Amphioxus). 



In fig. 6 (a longitudinal section of the chick-embryo of 

 52 hours), the first, i, and second, 2, cerebral vesicles have 

 expanded and approximated, the interspace is reduced to the 



* lb. p. 54. 



