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The External Jugular Vein. (Plate 45.)
The external jugular vein is formed, as in Rana, by confluence of lingual and mandibular veins. The mandibular vein takes its origin in the lining of the anterior ventral region of the maxilla, and runs backward along the whole length of the bone. A number of small tributaries enter it on either side. At the posterior extremity of the maxilla, the mandibular vein curves slightly inward and divides into two channels, which pass transversely across the body. The anterior channel is joined by a vein draining the anterior of the
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shoulder, while the other divides again into two. Shortly before the point of union with the lingual vein, all three vessels unite again to form a single vein, which, after joining with the lingual vein, curves back close to the heart, to enter the ductus Cuvieri. As it passes close to the heart, the left external jugular vein receives from the truncus arteriosus a small vessel which apparently corresponds to the vena bulbi anterior of Rana. The lingual vein is formed by a number of small vessels draining the tongue and hyoid. It passes directly back to unite with the mandibular vein.