PLATE 2 



EXPLANATION OF FIGURES 



5 Posteroventral view of a wax reconstruction of the caudal poition of the 

 pharynx and associated aortic arches of an embryo coot of six days. X 107. 



6 Posterodorsal view of a wax reconstruction of the caudal portion of the 

 pharynx of an embryo Forster's tern of six and one-half days. X 107. A.a.3,5,6, 

 fourth, fifth, and sixth aortic arches; A.dor., dorsal aorta; .4. p., pulmonary artery; 

 A.V., ventral aorta; C.ph.d., common pharyngeal diverticulum; Oes., oesophagus; 

 Tr., trachea; Ul.h.. ultimobranchial body; V.p.4,5, fourth and fifth visceral 

 pouches. 



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