348 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
venosus, open into it together on the left side. In order to accomplish 
this, the vein from the right fore limb makes a curve around the ven¬ 
tricle of the heart (pi. 23, fig. 1). This seems to be a constant feature, 
and fits in with the movement of the sinus venosus to the left side, first 
described by Hopkins, in 1896. 
The arterial system may be traced from the truncus arteriosus where 
three arches arise on each side instead of four (pi. 23, fig. 1; pi. 24, fig. 
3; pi. 25, fig. 5). My results on this point coincide with those of 
Bethge in the case of Spelerpes. 
The first arterial arch gives rise to the arteria carotis, which sends off 
on the ventral side an arteria carotis externa, and then continues 
around the esophagus to the dorsal side as arteria carotis interna, and 
thence into the skull to the brain (pi. 24, fig. 3; pi. 25, fig. 5). 
The second arch forms the aorta, but first gives off three branches 
on each side: an arteria occipitalis, an arteria maxillaris externa, and 
an arteria vertebralis collateralis (pi. 25, fig. 5). 
The occipital artery arises on the dorsal side and courses anteriorly 
near the inner margin of the eyeball (pi. 25, fig. 5). 
The external maxillary artery branches off from the second arch on 
each side, nearer the lateral region, passes outward and forward, giv¬ 
ing off a branch to the dorsal wall of the esophagus and pharynx (pi. 
24, fig. 4), and then divides to send one branch to the lower and one to 
the upper jaw (pi. 23, fig. 1). 
The arteria vertebralis collateralis arises from the dorsal side, nearer 
the median line than the external maxillary (pi. 25, fig. 5). It sends a 
branch to the skin at the side of the neck, and then passes posteriorly 
close to the vertebral column. It sends branches at each vertebra to 
the muscles of the dorsal and ventral body wall and skin. The two 
arteriae vertebrales collaterales communicate by means of nine or ten 
branches, between fore and hind limb regions, with the aorta. The 
first one or two of these branches pass from the aorta in an anterior 
instead of a posterior direction (pi. 25, fig. 5), a curious fact that was 
noted by Bethge in Spelerpes. It would seem to hinder the flow of 
blood from the aorta, unless the blood might flow in those branches 
from the arteriae vertebrales collaterales to the aorta. 
The two radices aortae unite to form the aorta at a point dorsal to 
the ventricle of the heart. The aorta in its posterior course gives off 
the following vessels: two arteriae subclaviae (pi. 23, fig. 1; pi. 24, 
fig. 3; pi. 25, fig. 5), each of which in turn gives off posteriorly an 
arteria sternalis (pi. 23, fig. 1); four arteriae gastricae (pi. 24, figs. 3, 
