No. 2.— Note on the Carotids and the Ductus Botalli of the 
Alligator. By C. B. Davenport.) 
Tue carotids of the Alligator, as is well known, usually present in 
the adult an unsymmetrical condition. From the right aortic root two 
branches (a and 0b) arise close together. Of these, one goes to the left, 
the other to the right side of the body. The left vessel (a) gives rise 
first to a large artery (1) running on the dorsal side of the cesophagus 
to the head ; secondly, to a smaller one (2) running alongside the neck, 
sending branches to the cesophagus, trachea, and muscles of the body 
wall, and anastomosing behind the occiput with a branch of 1; and, 
thirdly, to a vessel (3) going to the fore limbs. Other smaller vessels 
we may for present purposes neglect. The right vessel (6) gives rise to 
all that the left does excepting the equivalent of 1. 
Concerning the homology of these vessels with those of other Reptiles 
and of Birds, there has been much difference of opinion. Rathke (757, 
p- 91) designated the vessels a and 6 arteria anonyma. He called 1 
art. subvertebralis, and from embryological data he interpreted it (as 
defined in the preceding paragraph) as follows. The right and left com- 
mon carotids arise separately, and later fuse along the middle of their 
extent, but remain separate at their proximal and distal ends. Secon- 
darily, the right proximal root degenerates, and is thus absent in the 
adult. 
By “common carotid,” Rathke implies an homology with a vessel of 
this name in Lizards. The latter is morphologically eqnivalent to the 
ventral distributing trunk between the third and fourth arterial arches in 
Rathke’s well known type scheme of the arterial arches. The unfused 
distal ends of the common carotids each branch at the occiput to form 
vessels homologous, in his opinion, to the internal and external carotids 
of Mammals. 
Fritsch (’69, p. 705) later maintained that the a. subvertebralis is an 
a. carotis primaria, i. e. produced by a drawing out of the a. anonyma, 
1 Contributions from the Zoélogical Laboratory of the Museum of Comparative 
Zoology, under the direction of E. L. Mark, No. XXXIV. 
VOL. XXIV. — NO. 2. 
