THE AORTA OF THE RABBIT 
305 
intervals as represented in figures 8 and 9. The intercostal artery 
in the last case is really a branch of the innominate, and has no 
connection with the subclavian. Usually the superficial cervical 
artery of this side as in the normal condition is a branch of the 
transverse scapular artery, but in two cases is was greatly dis- 
placed; one originating from the subclavian (Fig. 3), and an- 
other curiously entering the common junction of the intercostal- 
mammary vessels as shown in figure 10. In one case the trans- 
verse scapular artery originates as a branch of the vertebral well 
cephalad of the latter’s junction with the subclavian, as in figure 
8, although in two other specimens this condition is barely sug- 
gested in the close proximity of the origins of the two vessels, as 
in figure 9. 
The manner of branching of the two carotid arteries from the 
innominate is of interest although not more variable than might 
be expected. In the majority of specimens showing differences 
in other respects the two carotid arteries branch well up on the 
innominate. In several cases the point of origin of the left 
common carotid artery is close to the curve of the aorta and in 
three cases (Figs. 6, 8 and 10) the junction is really on the arch, 
thus giving rise to an additional vessel in these cases as in- 
dicated above, which simulates very closely that found nor- 
mally in the human. Three individuals (Figs. 7, 9 and 10) show 
the formation of a thyreoid ima so-called, a small vessel arising 
on the innominate between the right and left common carotid 
arteries, which passes forward to the thyreoid gland and gives 
off small vessels to the neck muscles of the region and to the 
trachea. . Its point of . origin varies somewhat in the three animals 
but morphologically it bears the same position as has been de- 
scribed for a similar vessel in the human (McMurrich,^ p. 511), 
that is, it passes forward from the innominate between the com- 
mon carotid arteries of either side. It should be said, however, 
that since the common carotids of either side in man differ 
slightly in- their points of origin from those in the rabbit, the 
formation of this vessel in the rabbit does not contribute to the 
formation of a fourth vessel arising from the arch of the aorta, 
as is the case in man, but does form a fourth vessel from the 
innominate. In a single case, as shown in figure 11, the arch 
of the aorta gives rise to but one vessel, an innominate, which 
passes cephalad for some distance before it breaks to form, first, 
the left subclavian, and a little farther forward the left common 
carotid artery, and the brachio-cephalic artery. This peculiar 
