332 



vessel has entirely disappeared, excepting, perhaps, a slight spur from 

 the ventral artery at their point of former junction. 



To briefly summarize, it appears: first, that in the chick, the 

 earliest circulation to the wing region (from the third to the sixth 

 day) is derived from the dorsal Aorta, and that the main vessel of 

 this circulation corresponds to the Subclavian in the mammals; 

 second, that a secondary wing circulation, derived from the ventral 

 end of the third arch, not existing previous to the sixth day, is at 

 that time established, and that both vessels carry blood to the region 

 of the wing for a time; and third, that at some time in the latter 

 part of the seventh day, or the first part of the eighth, the primary 

 vessel atrophies and disappears, while the ventral artery increases in 

 size, and develops into the adult condition of the Subclavian. 



If, as HocHSTETTER suggests, the primary Subclavian represents 

 a modified segmental artery, we should recognize, I think, that it is 

 only the lateral portion of such an artery, because, as my preparations 

 show, the primary Subclavian and the dorsal portion of the Segmental 

 artery arise independently. Very soon, these two vessels become 

 united, and, by a further coalescence of the combined primary sub- 

 clavians and Segmental arteries, those of both sides are caused to 

 spring from a single median stem from the dorsal Aorta. 



Bibliography. 



Baer, K. E. v., Burdach's Physiol., Bd. 2, 1828, Tab. 4. 



Rathke, H., Untersuchungen über die Aortenwurzeln und die von ihnen 



ausgehenden Arterien der Saurier. Denkschr. d. K. Akad. d. Wiss. 



Wien, Bd. 13, 1857. 

 Sabatiek, Transformation du Systeme aortique dans la serie des Verte- 



bres. Ann. des Sei. nat., Ser. 5, T. 19, 1874. 

 Brenner, A., Ueber das Verhältnis des Nervus laryngeus inferior vagi 



zu einigen Aortenvarietäten des Menschen und zu dem Aortensystem 



der durch Lungen athmenden Wirbelthiere überhaupt. Arch. f. Anat. 



u. Physiol., 1883. 

 Foster and Balfour, The Elements of Embryology, 1874. 

 Mackay, John Y., The Development of the Branchial Arches in Birds, 



with special Reference to the Origin of the Subclavians and Carotids. 



Phil. Trans, of the R. Soc. of London, Vol. 179, 1888, 

 HocHSTETTER, FERDINAND, Ueber den Ursprung der Arteria subclavia 



der Vögel. Morph. Jahrb., 1890. 



