DEVELOPMENT OF HUMAN PHARYNX 339 



ever interpreted, the tongue early complicates the development 

 of the pharynx. 



Finally there must be mentioned the evident and marked 

 modification of the dorsal region (epi-hyperbranchial) of the 

 pharynx by the growth of that portion of the head as epitomized 

 by the brain-tube, whose growth in length and bendings has 

 clearly been accompanied by corresponding effects on the adja- 

 cent pharyngeal structures. The expansion dorsally, as con- 

 trasted with the ventral restriction of the pharyngeal region, 

 is expressed in the arrangment and relations of the external 

 gill clefts, as illustrated in any typical lateral view of a mam- 

 malian embryo. 



DEVELOPMENTAL TRANSFORMATIONS OF THE 

 HUMAN PHARYNX 



From the above brief considerations it will be apparent that 

 the pharynx of mammals (and man) departs widely from the 

 primitive conditions and relations that the region must have 

 presented in the vertebrate ancestor. In the examination of 

 the growth transformations and shiftings it has thus been neces- 

 sary to keep in mind the fundamental morphology of the region, 

 since it constitutes the basis to which the growth transformations 

 must be referred. 



The different growth relations of the cephaHc portion of the 

 pharynx and the caudal portion of the pharynx (well illustrated 

 in the figures of plates 1 to 4, particularly 14, 15 and 21), the 

 former being characterized by its expansion and participation 

 in the growth of the head, the latter by its concentration and 

 ventro-caudal growth, soon differentiates the pharynx into two 

 fairly well defined regions, for which Mayr ('12) has proposed 

 the names of 'propharynx' and 'metapharynx' ('laryngopharynx') 

 respectively. The investigation of the growth shiftings in the 

 domain of the pharynx thus faUs quite naturally into three 

 parts: (1) that of the dorsal wall and cephalic portion, including 

 the first (and second) branchial arches and the first and second 

 pouches; (2) that of the tongue and the corresponding portions 

 of the pharyngeal floor; (3) the caudal and ventral portions in- 



