DEVELOPMENT OF HUMAN PHARYNX 335 



terms here used are those employed by Grosser, Branchial 

 is employed in preference to pharyngeal, pouch (sacculus) is 

 used for the entodermic outpocketing; while cleft (fissura) is 

 employed to designate the ectodermal insinking. Each pouch 

 cleft, arch, parathyreoid, thymus, etc., in the series, is designated 

 by number (I-V). The term 'Complex III' includes the struc- 

 tures appearing in the transformation of the third pouch, while 

 Complex IV or 'caudal pharyngeal complex' denotes the struc- 

 tures associated with the fourth pouch. As the complex, in the 

 process of growth, becomes separated from the pharynx, the 

 attenuated connection is designated as 'ductus pharyngeo- 

 branchialis' (III, IV), while the corresponding diminishing 

 connection with the ectoderm is termed 'ductus branchialis' 

 (II, IV), the 'ductus cervicalis' being the connection of the 

 cervical vesicle with the ectoderm. 'Parathyreoid' is employed 

 in preference to 'epitheUal body.' 



Material and methods 



The study was begun in 1911 in the Department of Compara- 

 tive Anatomy of the Harvard Medical School and continued 

 at Ithaca, New York, and is based upon the human embryos in 

 the embryological collection at the Harvard Medical School, 

 supplemented by those in the collection at Cornell University, 

 many of which were placed at my disposal by Prof. S. H. Gage, 

 whose generous ' assistance I am glad to acknowledge. My 

 studies were futher greatly assisted by the willingness of Prof. 

 Minot and Prof. Lewis to loan me from time to time embryologi- 

 cal series from the Harvard collection. The list of embryos 

 consulted is given in table 1. The ones more particularly studied 

 include those modelled, namely, 3 mm., 5 mm., 7.5 mm., 9.4 

 mm., (2) 10.0 mm., 13.0 mm., 14.5 mm., 16.4 mm., 18.2 mm. 



MORPHOLOGICAL PLAN OF THE PHARYNX 



In considering the developmental changes in such a region 

 as the pharynx, from the viewpoint of its ancestral character 

 as a branchial chamber, it is of obvious importance to obtain 



