514 



FRANK REAGAN 



Clt. 



Pr.p.c. 



Mes.c 



Sin.pr. 



Fig. 16 Reconstruction of the glandule thyroidienne and the ])ie-pulmonic 

 caecum of an 8 mm. pig. The planes of the cut surfaces (represented as striated 

 areas in the figure) arc practically frontal. The lower (i.e., more anterior) plane 

 pa ses through the glandule thyroidienne. The upper (posterior) plane passes 

 thiough the pre-pulmonic caecum. The figure is slightly diagramatic. 



ADDENDUM 



I regret very much to say that the excellent work of Reinke (E. E. Reinke, 

 Anatomical Record, December 1910) had entirely escaped my notice until the 

 present work was sent to press. On the whole, his results agree very closely 

 with my own. The fifth arch of his 6 mm. pig seems more degenerate than 

 that of my figures 1 to 7. It may be questionable that the vessel had existed 

 at all more typically than at the stage at which the embryo was killed. Its 

 ventral origin is perhaps from a more dorsal point; fiom his fig. 2, the calibre 

 of the fifth arch seems relatively smaller, and its contour is less regular. The 

 conditions in general, support admirably my contention that the fifth vessel 

 does not essentially have the dorsal extremity of the pulmonic arch for its 

 distal termination, since the connection with the aortic root is much the larger. 

 The double nature of the glandule thyroidienne of Reinke's fig. 1 (labeleil 

 Pouch Four) strongly suggests its comparability to the anterior pouches. In a 

 few instances I liavc observed the presence of five ectodermal grooves, but the 

 parallelism between these and the i)resence of a fifth vessel does not seem 

 constant. 



Even with an additional consideration of this valuable contribution, I still 

 believe the existence of a new arch to be somewhat questionable, although 

 there is mucli evidence in favor of it. 



