DEVELOPMENT OF HUMAN PHARYNX 357 



independently of the second cleft upon the ectoderm behind 

 the cleft, i.e., at the point characteristic for the epibrachial 

 placode II. Similar epitheUal prolongations in continuity with 

 the ectoderm in the territory of the second cleft have been des- 

 cribed in other mammals, e.g., in the rabbit by Piersol, ('88) in 

 the pig by Zottermann ('11) and Badertscher ('15), in the guinea- 

 pig by H. Rabl ('13), under the name of ductus branchialis. It 

 is not quite clear, however, what the morphological value in these 

 cases may be, and inasmuch as it is an expression of persistent 

 ectodermic attachment under growth expansion, its value may 

 well vary in different forms. 



Whether or not that portion of the ductus branchialis II that 

 adjoins the second pouch persists so that ectodermal cells be- 

 come incorporated with the entodermal cells, was not determined 

 but exists as a possibility. In the same manner, the fate of the 

 cells of the vesicles that maintain their association with the 

 ganglion petrosum and ganglion nodosum is problematic. The 

 connection of the vesicle derived from the ductus branchialis 

 II with its ganglion (vesicula branchialis II, figs. 21-22) seems 

 not so intimate as does the connection of the cervical vesicle 

 with the ganglion nodosum, where the epithelium merges with 

 the ganglion wdthout sharp boundary and all appearance of a 

 close fusion. Whether the characteristic elements of the gang- 

 lion, neuronal or other, receive from the placode or subse- 

 quently from the vesicle, augmentations, could not be definitely 

 determined, although the histological appearances and relations 

 suggest strongly that such may be the case — a, conclusion simi- 

 lar to that reached by Hammar, and independently formed. 

 Whether a definite group of neurones, the gustatory, have this 

 placodal origin, from the epibranchial placodes — as Landacre 

 concludes from his interesting study of the developmental rela- 

 tions in Lepidosteus and Amiurus — can of course be still less 

 determined from the material and methods of the kind used in 

 this investigation; it is a study quite apart from that ^of the 

 pharynx and its derivatives. 



The cervical vesicle is not only partly imbedded in the lower 

 end of the ganglion nodosum, but in the mechanics of growth 



