PLATE 3 



EXPLANATION OF FIGURES 



18 Ventral view of the model of the pharyngeal epithelium in a 14.5 mm. 

 human embryo (No. 1003, Harvard Embryological Collection). X 40. 



19 Dorsal (posterior) view — as referred to the embryo's body — of a model 

 of the pharyngeal epithelium in a 9.4 mm. human embryo (No. 1005, Harvard 

 Embryological Collection). One-half of the pharynx only is shown. The ecto- 

 derm upon the left side is included in the model, the inner surface being here 

 revealed. X 50; reduced 1/3. 



20 Lateral view of the caudal portion (metapharnyx) of a model of the pharyn- 

 geal epithelium in a 13 mm. human embryo (No. 26, Cornell University Col- 

 lection). X 75. 



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