20 The Cephalic Veins and Sinuses of Reptiles 
close to the wall of the tympanic cavity and on the median side of the 
chorda tympani. Just before it reaches the roof of the tympanum the 
vein meets the vena jugularis interna which it enters from a lateral 
direction. 
e. VENA MANDIBULARIS. 
(v. m., Text. Figs. 2 and 3). 
The vena mandibularis of Lacerta agilis is referred to by Grosser and 
Brezina, 95, in their description of embryo VI ‘(head 3.1 mm.) under 
the name vena maxillaris. ‘The vein is considered a temporary struc- 
ture, however, for in their description of a later stage (embryo XIV, 
head 4.1 mm. long) it is said to have found a substitute in the vena 
trachealis. 
In my sections of adult Lacerta agilis and other lizards the vena 
mandibularis is well developed, though it is a vein of only moderate size. 
Under typical conditions, such as we find in Cnemidophorus, the vena 
mandibularis is formed by the union of two veins, the vena mandibularis 
interna and vena mandibularis externa, which unite at a point dorsal 
to the mandible and posterior to the tympanum. In Lacerta the vena 
mandibularis interna fails to joi the vena mandibularis externa, but I 
shall, nevertheless, consider the vena mandibularis as beginning at the 
same point where it begins in Cnemidophorus. From this point, which is 
designated above, the vena mandibularis of Lacerta runs dorsad toward 
the vena jugularis interna, which it enters from a lateral direction, a 
short distance anterior to the mouth of the vena cerebralis posterior 
(compare Text Figs. 2 and 3; Fig. 3, Plate I). 
In addition to the vena mandibularis externa, which is described be- 
low, the vena mandibularis of Lacerta receives two other tributaries 
(Text Fig. 2): a vena wsophagea and a vena tympanica posterior. The 
former (v. 0.) drains the mucous membrane of the cesophagus, together 
with the adjacent muscles. The vena tympanica posterior (v. t. p.) 
receives blood from the floor and posterior wall of the tympanic cavity. 
It runs caudad along the ventral margin of the tympanic membrane and 
joins the vena mandibularis a short distance above the posterior end of 
the mandible. 
The internal and external mandibular veins must now be described. 
1. VENA MANDIBULARIS INTERNA (v. m. 1., Text Fig. 2).—The vena 
mandibularis interna of Lacerta is, for the most part, an intraosseous 
vein, which begins in the anterior part of the mandible and passes back- 
ward on the dorsal aspect of Meckel’s cartilage in company with the 
