26 The Cephalic Veins and Sinuses of Reptiles 
joint; it unites with the trunk vein just before the latter bends mesad to 
enter the vena jugularis interna. 
In its relations and drainage the vena jugularis externa resembles in 
a general way the like-named vein of the higher vertebrates. On the 
other hand it seems to correspond to the anterior part of the vena cutanea 
magna of amphibians. If the latter view is correct, it is not improbable 
that the vena jugularis externa of higher forms has been derived from 
the vena cutanea magna of amphibians, the posterior part of the latter 
vein having been reduced as the cutaneous respiration declined in 
importance. 
B. THE TERRITORY OF THE VENA TRACHEALIS. 
The trunk of the vena trachealis has been described by Parker, 84, 
under the name vena jugularis externa, and by Vogt and Jung, 89-94, 
p- 714, as “die unpaare Kopfvene,” vena cephalica impar. The system 
of the vena trachealis has been worked out in late embryos of Lacerta, 
in which the larger vessels are presumably in the adult condition. In an 
embryo which is apparently ready to hatch (head 5.2 mm. long) the vena 
trachealis (v. ¢t., Text Fig. 3) is an unpaired vein which runs along the 
right side of the trachea and enters the right vena cava superior di- 
rectly median to the mouth of the vena jugularis interna. The vena 
trachealis is formed near the caudal end of the hyoid bone by the union 
of the right and left tracheal veins. Behind this point the vena trache- 
alis receives no large tributaries, but numerous small veins enter it from 
the trachea, cesophagus, thymus gland, and the ventral neck muscles. 
The right and left tracheal veins require a more extended description. 
a. VENA TRACHEALIS SINISTRA. 
(wit. +s,’ Lext Bie<3:) 
The vena trachealis sinistra begins as a small vein lateral to the body 
of the hyoid bone. Running directly caudad, the vein passes above the 
ventral end of the anterior hyoid cornu and receives the vena buecalis 
sinistra. It then crosses the middle line above the trachea and unites 
with the vena trachealis dextra. 
The vena buccalis sinistra drains the floor of the mouth lateral to the 
tongue, larynx, and the anterior part of the trachea. The rostral part 
of the vein extends in a nearly sagittal direction, about midway between 
the tongue and the mandible. Posteriorly the vein bends toward the 
