342 B. F, KINGSBURY 



geal furrow by Grosser) figured by him before the definite appear- 

 ance of the thyreoid outpocketing (in embryo Keb., N. T. No. 

 3) it apparently has nothing to do. This groove, which appears 

 thus early extending caudally from the thyreoid whose early 

 anlage it includes, may tentatively be regarded as a hypo- 

 branchial groove, in its cephalic part at least. Subsequently 

 with the expansion of the pharynx and the growth of the neighbor- 

 ing heart and pericardium, it becomes obliterated. 



With the expansive development of the heart within the pri- 

 cardium, the branchial arches and truncus aorticus, begin the 

 important and characteristic transformations of the pharynx, 

 ending only with the assumption of its adult morphology. It 

 is generally assumed that the branchial pouches possess ventral 

 and dorsal extensions or diverticula. Ventral diverticula are 

 shown for several of the pouches in figures 12, and 13, while 

 small dorsal projections exist in the 7.5 mm. embryo (figure 14). 

 Although these are usually considered as branchial extensions 

 of intrinsic significance, careful study of their relations indicates 

 that in their shape and extent they are also a partial expression 

 of the growth relations of the region and are afi'ected by the 

 adjacent arches whose size and direction they in a degree indi- 

 cate; this readily appears in models such as those represented in 

 figures 12, 13 and 14, in which the impressions of the arches, 

 as negative pictures, are shown in the molding of the epithelium. 



In figures 12 and 13, which might be compared with similar 

 figures, such as figure 22 of Grosser ('11 a) and figure 7 of Ingalls 

 ('07) and figure 6 of Coulter ('09) for the cat, there is shown the 

 'thyreoidipetal' direction of the ventral branchial diverticula 

 I, II, III and IV. This direction of the pockets of course is 

 also in conformity with that of the arches. As important 

 constituents of the arches are the branchial aortic arches, 

 which arise from the truncus aorticus, so that the region where 

 the axes of these ventral branchial diverticula center might 

 be described with equal propriety as being that of the truncus 

 aorticus or its bifurcation (cf. also figures 1, 2. 3). In front of 

 (cephalad of) the bifurcatio trunci aortici and in close apposition 

 to it is the thyreoid gland. In embryos of 5 to 7 mm. length 



