DEVELOPMENT OF HUMAN PHAEYNX 359 



the precocious and marked growth of the second arch, which as 

 an opercuhim encroaches upon the boundaries of the sinus and 

 finally causes its obliteration. The rather deep insinkings of 

 ectoderm along the lines of the branchial clefts in the precervical 

 region appear to be withdrawn with the growth of the mesoderm, 

 although the inclusion and degeneration of portions cannot be 

 excluded (figs. 9-11). 



Larynx 



Although the pharyngeal transformations that determine 

 the development of the larynx and its related structures are but 

 a part of the growth of the entire region and are affected by the 

 shiftings in the lower pharynx, they are omitted from the present 

 paper, since the points of interest still undetermined relate more 

 to the mesodermic arches than to the epithelium and its deriva- 

 tives, whose explanation is the question considered in the present 

 paper. 



PHARYNGEAL DERIVATIVES 



In the foregoing paragraphs I have attempted to describe in 

 a concise way the morphological transformations of the branchial 

 epithelium, entoderm and related ectoderm, as but the expres- 

 sion of one side of the growth of the region with its varied stresses 

 and strains and shiftings, which in their totality produce the 

 anatomical relations of the adult. But a moment's reflection 

 is necessary to establish the conclusion that it could not be 

 otherwise, and the criticism maj^ perhaps be offered that any 

 morphological analysis of the regional growth is superfluous, 

 as it can only establish conclusions that are self-obvious and 

 which might be arrived at from a priori reasoning; that is, it 

 is simply a description of changes that inevitably follow from 

 the relations of parts in the region which can establish nothing 

 in the way of explanation or build a foundation on which the 

 explanations may be subsequently worked out. Such a criticism, 

 however, in the specific instance in hand, has weight only on 

 the assumption that there are certain pharyngeal organs pre- 

 determined in development, 'pharyngeal organs' whose growth 



