PLATE 1 



EXPLANATION OF FIGURES 



12 Ventral view of a model of the epithelium of the pharynx in a 5 mm. 

 human embryo (Buxton embryo, Xo. 5, Gage Collection). X 50. Upon the 

 right, the ectoderm is shown in position, cut surfaces are indicated by cross 

 lining. 



13 Ventral view of a model of the pharyngeal epithelium in a 7.5 mm. 

 human embryo (No. 256, Harvard Embrj^ological Collection ). X 60. Only the 

 left half was modelled in the anterior portion of the pharynx. 



14 Lateral view of the same model. The ectoderm is removed, and the sur- 

 faces of contact are indicated by line shading, as in figure 12. X 60. 



388 



