Veins from the Skin.
If fig. 1 be compared with Ecker's* it will be seen that the veins coming from the skin differ widely in the two frogs. According to Ecker, with the exception of three pairs of parietal veins near the posterior end of the abdomen, all the blood from the skin is returned through the large cutaneous veins.
Now, in Hyla aurea there are four centres from which the blood from the skin is returned, and this is done by four distinct pairs of veins—namely, the external jugulars, the cutaneous, the parietals, and the pelvico-cutaneous—the first three being especially noticeable.
1. The external jugular veins (e.j.) are a pair of very large and often much-twisted vessels running across the body from the angles of the jaws towards the median line just above the pectoral girdle and then disappearing through the body-wall. Some of their branches—namely, the mandibular and several other large veins—bring in the blood from the skin around the head and shoulders.
[Footnote] * Ecker's “Anatomy of the Frog,” Eng. trans., p. 244, fig. 161.
2. The cutaneous veins (c.) are a pair of medium-sized vessels bringing blood from the skin for a short distance posterior to the arms. Each vein is composed of a number of small branches, which arise from the skin; they unite and form the large vessel which, after running for a short distance across the ventral body-wall, disappears just below the pectoral girdle.
3. The parietal veins (p.) are a pair of veins often as large as the cutaneous, and they bring blood from the skin about half-way down the abdomen. They, like the cutaneous veins, are much branched, and the main trunk runs across the ventral body-wall and soon disappears into the body-cavity. Their course as they run to meet the anterior abdominal vein can often be traced through the body-wall.
4. The pelvico-cutaneous veins (p.c.) are a pair of veins bringing blood in from the skin around the pelvic girdle. Each vein is composed of several branches, and these uniting run through the body-wall near the junction of the legs to the trunk. If the body-wall be opened it will be seen that they connect with the renal portal veins just after the bifurcation of the femoral veins. Near the mid-ventral line and just anterior to the pelvic girdle there are often one or two very small, short veins running out to the skin.