Page 462. 
166 THE CAROTID ARTERIES OF BIRDS. 
the left innominate springs, is less than in the vessels it connects; 
consequently the current there tends to stagnate; but a tendency to 
stagnate in blood is a tendency to coagulation, as is seen in the 
proximal end of a ligatured arterial trunk; and the tendency to 
coagulation is a tendency to obliteration of the vessel in which the 
coagulation occurs ; consequently the right carotid must tend to dis- 
appear, which it does in nearly every case. Since this explanation 
occurred to me, I have not had the opportunity of examining any of 
the birds in which the right artery persists after it has fused with the 
left, to see if there is any peculiarity in their vascular arrangement 
which will account for its persistence. When the carotids do not 
blend there is evidently no reason why either should disappear; and 
when they do join, the presence of a large pectoral and subclavian 
branch from each innominate does not alter the problem; it only 
indicates that the obliteration must occur distad of it, as is the case. 
The following list includes all those species of birds in which I 
have had the opportunity of observing the disposition of the carotid 
arteries. They are arranged nearly according to the classification 
adopted in Mr. Sclater’s revised List of the Vertebrated Animals in 
the Gardens of this Society. 
PASSERES. 
All the Passeres examined possess the left carotid only. 
Species examined. 
OSCINEs. 
a. Oscines dentirostres. 
Turdus merula. 
grayt. 
Sylvia hippolais. 
Luseinia vera. 
Erithacus rubecula. 
Pratincola rubetra. 
Ruticilla phenicura, 
Myjiadestes obscwrus. 
Sialia wilsonit. 
Troglodytes parvulus. 
Mniotilta varia. 
Oinclus aquaticus. 
Motacilla flava. 
Hirundo rustica. 
Anthus pratensis. 
Parus major. 
Sitta ewropea. 
Lanius collurio. 
Sigmodus caniceps. 
Struthidea cinerea. 
Oriolus, sp. 
Artamus, sp. 
Graucalus mace. 
Dicrurus leucops. 
Muscicapa griseola, 
Ptilogonys cinereus. 
Ampelis garrulus. 
b. Oscines latirostres. 
Ohelidon urbica. 
