284 Herbert M. Evans. 



need not refer here to the details of such methods, since they will 

 be described adequately elsewhere. Recently Kuower^ has described 

 carefully a method of using glass bulbs in this connection, which 

 is very useful. 



Whatever the details of the procedure are, fine glass canulse, the 

 helpful binocular microscope, and living embryos comprise the essen- 

 tials. I used every possible channel as a starting place from which 

 to reach the general circulation. The veins, the liver, and the heart 

 itself were successivly chosen only to be abandoned. The larger 

 arteries, however, permitted the employment of great pressure with- 

 out danger of rupture. Thus the entire vascular system could be 

 filled with the minute carbon particles of the injection mass (India 

 ink), which, passing through arteries and capillaries, and again 

 streaming into the heart by the veins, are pumped out again into 

 the circulation. The more perfect of these beautiful specimens 

 were subjected to detailed study and at length convinced us that 

 in some instances we had attained a complete injection. The endo- 

 thelial sprouts themselves were everywhere filled to their tips. We 

 beheld the growing vascular system ! 



The revelations which such injections have made are in no place 

 more striking than in the case of the origin of the chief vessels to 

 the limbs; the femoral and the subclavian arteries. The results 

 here, too, are of peculiar interest, inasmuch as the latter vessels 

 have been studied with most painstaking care and, in the recent work 

 of Miiller and of Rabl, have already been traced to a very primitive 

 condition. 



The present communication deals chiefly with the first blood- 

 vessels which grow into the anterior-limb buds, and is almost entirely 

 based on a long series of chick and duck embryos, though I have 

 also studied the early mammalian limb and the arm bud in man in 

 this connection. 



Before presenting these observations, however, some account of the 

 literature on the origin of the avian-subclavian artery will not be 

 out of place. 



'Kiiower, II. McE. "A New and Sensitive Method of Injecting the A^essels 

 of Small Erahryos, etc." Anat. Record, Vol. II, No. 5, August, 1908. 



