PLATE 1 



EXPLANATION OF FIGURES 



3 Postero ventral view of a wax reconstruction of the caudal portion of the 

 pharynx and the associated aortic arches of an embryo gallinule of four and one- 

 half days. X 150. 



4 Posteroventral view of the caudal portion of the pharynx of a chick embryo 

 of five and one-half days. X 150. A.a4,5,6, fourth, fifth and sixth aortic arches ; 

 A. p., pulmonary artery; A.v., ventral aorta; Oes., oesophagus; Tr., trachea; 

 Ul.b., ultimobranchial body; V.p.4,5, fourth and fifth visceral pouches. 



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