340 B. F. KINGSBURY 



eluding the third and fourth pouches and clefts and the second 

 cleft, together with the thyreoid gland. It is mainly the last 

 section of the pharynx development which is considered in the 

 present paper. While it is the author's plan to consider at a 

 subsequent time some of the growth changes in the territory 

 first mentioned, no attempt is contemplated to add to the knowl- 

 edge or interpretation of the tongue, inasmuch as it is felt that 

 there is not a great deal to add to the published work of Kallius 

 and others, save in the earliest transformations, material for which 

 is not at hand or at present easily available. 



Closely interwoven with the developmental changes which 

 the lower portion of the pharynx undergoes, are (1) the develop- 

 ment of the lungs (larynx and trachea) and (2) the develop- 

 ment of the heart and aortic arches, mentioned above as of 

 modifying influence in the development of the pharynx. To 

 these should be added a third modificatory factor, the epi- 

 brancial placodes; while the neck-bend as an expression of cranial 

 growth relationships and siirdlarly, to a certain degree, the dif- 

 ferent postpharyngeal growth tendencies, affect the morpho- 

 genesis of the region. 



The precocity in the development of the lungs has already 

 been referred to. In a 2.5 mm. embryo (Robert Meyer, No. 

 300) Grosser ('11 a, '11 b) has described its first appearance as 

 well caudad or the branchial region at a stage in which the 

 laryngo-tracheal groove extends to the caudal limit of the ^meso- 

 branchial field.' With the subsequent development of the glot- 

 tideal opening and of the branchial region, the laryngo-tracheal 

 groove is described by Grosser (p. 463) as "extending farther 

 into the mesobranchial field between the medial ends of the 

 fourth and (later) even the third branchial arches." This 

 intrusion of the laryngeal opening into the branchial region of 

 the pharynx might, I beheve, be better described as essentially 

 a 'telescoping' or intussusception, due to the expansive cephalo- 

 caudal differential growth of the branchial pharynx and the 

 precocious development of the lungs (trachea and larynx), 

 in the nature of a heterochronia. The attendant alteration in 

 the morpholog^^ of the region may be illustrated by means of 



