212 Henry Fox " 



tion, and at the same time carries with it the attached adjacent parts. 

 As already mentioned, the antero-lateral margin of the second poucTi 

 is continuous anteriorly with the latero-posterior border (S.T.T.) of 

 the first pouch. At first the two join at a considerable angle, but as 

 this border of the first pouch is carried outwards by the growth of the 

 pouch, the attached antero-lateral border of the second pouch (Ton.F.) 

 follows it and thus the angle tends to become drawn out and the borders 

 to form a continuum. Consequently at this stage the antero-lateral 

 border extends diagonally outwards instead of inwards, as in preceding 

 stages. 



The lateral flexure of the antero-lateral margin causes it to arch 

 outwards above the underlying antero-lateral wall. The latter thus 

 forms a well-marked concavity, which is limited internally by the low 

 fold (later part of the alveolo-lingual sinus) connecting the ventral 

 diverticula of the first and second pouches. Owing to its inclined posi- 

 tion, this surface will henceforth be called ventro-lateral (Fig. 12, c. v.). 



Corresponding to the depressed condition of the ventro-lateral sur- 

 face, the dorsal surface, which is everywhere closely adpressed against 

 the underlying wall, is raised into a low dome-shaped convexity. The 

 latter I shall call the dorsal prominence (Fig. 10, D.Pr.). 



The ventral diverticulum (v. d. 2) is reduced to about three-fourths 

 of its former vertical extent. • This change I am inclined to attribute, 

 in part at least, to the outward extension of the antero-lateral portion 

 of the pouch. The latter would set up a tension in the remainder of 

 the pouch which would lead to a partial absorption of the diverticulum 

 into the adjacent portion of the pouch. A fact favoring the existence 

 of such a tension is the presence upon the ventro-lateral wall of a 

 narrow fold extending obliquely upwards from the base of the diver- 

 ticulum (Fig. 12). 



The lateral margin of the second pouch is now largely free from the 

 ectoderm, the connection with the latter persisting only in its more 

 ventral portion, where the corresponding ectodermal groove forms a 

 deep, vertical pit (Fig. 11). 



The pig of 14 mm. (ISTo. 65, Harvard series, Figs. 14-17) shows the 

 second pouch slightly reduced in vertical extent, but produced at its 

 ventro-lateral angle into a long, fine process (Fl.P.), the distal end of 

 which is attached to the ectoderm. Elsewhere the pouch is free and is 

 removed by a wide interval from the ectoderm. This condition is the 

 result of the rapid growth in thickness of the hyoid region. As the 



