214 Henry Fox 



Owing to the continued lateral extension of the dorso-lateral margin 

 (Ton.F.), the original lateral border now forms a continuum with it. 

 This leaves the dorsal apex as a minute protuberance at its posterior 

 extremity. 



The dorso-lateral margin shows no increase in length, but anteriorly 

 it has been carried farther outwards in consequence of the extension of 

 the tympanic pouch in that direction. It thus acquires a coiirse almost 

 in line with the postero-lateral margin (s. t. p.) of the latter. Only a 

 slight notch remains to indicate the dividing line between them. 



The ventral diverticulum (v. d. 3) has now nearly disappeared, 

 having been absorbed by the downgrowth of the ventro-lateral margins 

 of the pharynx. 



The features of the second pouch in the pig of 17 mm. are essentially 

 duplicated in cats of 10.7 mm. and 12 mm. 



A rabbit of 14 days (No. 157, Harvard series. Fig. 70) shows a stage 

 somewhat intermediate between that just described and the next. 



The same remark is also applicable to an 18 mm. pig (Series ]\P, of 

 my collection). 



In a pig of 20 mm. (No. 542, Harvard series. Figs. 23-27) the second 

 pharyngeal pouch is chiefly modified as regards length and direction. 

 As indicated by the fig-ures, these modifications are related to the ventral 

 (caudal) flexure of the posterior half of the pharynx. As already men- 

 tioned (see account of tympanic pouch), the tympanic pouch has at this 

 time become relatively fixed in position l)y the formation about it of 

 the related cartilages. Consec[uently, as the pharynx continues to bend 

 toward the ventral side, the attached second pouch tends to be drawn 

 out and flattened (Fig. 23). This process is also accelerated by the 

 continued deepening of the ventro-lateral margin of the pharynx. 



The hitherto jDrominent dorsal prominence is now reduced to a low 

 swelling located at the postero-internal angle of the tympanic pouch. 

 No lateral extension of this part of the pouch has taken place since the 

 17 mm. stage. Its middle and posterior portions, on the contrary, have 

 shrunken slightly, due probably to the tension produced by its elonga- 

 tion in the ventral direction and the continued downgrowth of the 

 adjacent ventro-lateral margin (A-L.F.) of the pharynx. 



Posteriorly the second pouch thus forms a low ridge situated on the 

 outer side of the ventro-lateral fold (= conjoined alveolo-lingual and 

 piriform sinuses). 



The shrunken filiform process is still recognizable. 



