and, beside returning blood from the lower jaw and tongue, it also returns it from the muscles of the shoulder, tympanic membrane, eye, nose, and the left side of the head generally. This latter group of organs is in Rana* drained by a large branch of the subclavian vein, called the cutaneous, but in Hyla aurea the cutaneous (fig. 1, c.) does not reach much above the forelimb.
It may also be noticed that the external jugular is not, as in Rana, wholly made up by the mandibular and lingual veins, but these are merely small branches joining on the main vein as it comes from the side of the head. If the skin from the side of the head be dissected off as in fig. 3 the small veins about the head that unite to form the external jugular can be seen.
The nasal vein (fig. 3, n.) runs from the external nares, near the edge of the upper jaw, and unites with the main trunk of the external jugular just at the angle of the jaws.
The orbital veins (fig. 3, o.) join the nasal as it passes the eye. They are usually two in number.
The tympanic vein (fig. 3, t.) is a vein bringing blood from the tympanic membrane.
There is a vein bringing blood from the dorsal muscles of the shoulder, and one bringing blood from the skin around the shoulder and head, which also join the external jugular near the angle of the jaws (fig. 3).
2. The Innominate Vein (fig. 2, in.).—This is the second and middle vein of the three that make up the left anterior vena cava. It is a very short vein, and is made up of two main branches—(a) internal jugular vein (fig. 2, i.j.), returning blood from the interior of the skull and the eyeball, and leaving the skull near the posterior border of the orbit; (b) subscapular vein (fig. 2, sa.) is a smaller vein than the former, and returns blood from the region of the scapular bone.
3. The Subclavian Vein (fig. 2, sub.).—This is larger than the innominate, but much smaller than the external jugular. It returns blood from the muscles of the shoulder and the forelimb. It is made up of the (a) brachial vein (fig. 1, br.), which returns blood from the arm, and, after entering the bodycavity, runs direct to join with the subclavian; (b) the musculocutaneous vein (fig. 2, m. and c., and fig. 1, c.) returns blood from the skin posterior to the arms, and some of the muscles of the shoulder. It does not, as in Rana, have anything to do with skin anterior to the fore-limbs or the head. The musculo vein returns blood from the muscles, and the cutaneous from the skin, as before described.
[Footnote] * Ecker's “Anatomy of the Frog,” p. 244, fig. 161.
II. Right Anterior Vena Cava.
This vein and its branches correspond to the left.
III. Posterior Vena Cava (fig. 2, p.v.c.).
This is a large median vein, returning blood from the kidneys and reproductive organs. It is formed by five or more pairs of renal veins, and then runs forward amongst the viscera, through the liver, on to the sinus venosus. Just after emerging from the liver a pair of hepatic veins join it.
The pulmonary veins are a pair of small veins, and are often very difficult to see. They return blood from the lungs, and run along its inner side to the heart, where they unite, and open into the left auricle.