Earliest Blood Vessels in Anterior Limb Buds. 287 



of the Anamniota, since this is also the vessel which occurs in both 

 the fish and amphibia. Thus this important paper emphasized 

 the fact that in all vertebrates possessing fore limbs, the primary 

 subclavian artery arises from the dorsal aorta. 



In 1905, C. G. Sabin,"^ working in Locy's laboratory, reworked 

 the subject and furnished us for the first time with good illustra- 

 tions of the origin and course of both the primary and secondary 

 subclavians in the chick. Sabin not only pushed the time of origin 

 of the primary vessel to a stage much earlier than Hochstetter had 

 suspected, i. e,, to the third, instead of the fifth, day of incubation, 

 but he also made another observation which must be considered an 

 important contribution to the subject. Sabin was the first to show 

 that the primary subclavian was not at first a branch of the dorsal 

 segmental artery but instead was primarily an independent out- 

 growth of the aorta and only secondarily came to be included as 

 a branch of the dorsal vessel. 



The admirable paper published in the summer of 1907, by Rabl,^ 

 was by far the most complete account we possessed of the subclavian 

 arteries in birds and it marked the discovery also of a new fact 

 of great importance, namely that the single primary subclavian is 

 itself preceded by a row of some three segmental subclavians. These 

 early segmental subclavians had been entirely overlooked. 



Rabl's research was based on a careful study of sections of duck 

 embryos. The account which he has given us is of the greatest 

 interest, for it indicates that the metamerism of the limb is as 

 distinctly expressed in its primitive vessels as it is in the nerves 

 and myotomes that enter into its structure, a point which was first 

 discovered by Erik Miiller" in selachians and in reptiles, and which 

 has been emphasized by the latter observer in several articles on the 

 arm V( 



'Sabin, C. G. "The Origin of the Subclavian Artery in the Chide." Anat. 

 Anz., Bd. XXVI, 1905, p. 317. 



*Rab], Hans. "Die Erste Anlage der Arterieu der vorderen Extremitiiten bei 

 den Vogeln." Arch. f. milj. Anat., Bd. 09, pp. .340-387. 



*Muller, Erilc. "Beitnige zur Morphologic des Gefasssystems." Anat. Hefte, 

 June, 1903 ; Dec, 1904 ; and Feb., 1908. 



