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The Cephahe Veins and Sinuses of Reptiles 
prooticus. From the sinus articularis the vena mandibularis interna 
runs caudad below the articulation, posterior to which it again forms two 
anastomoses, one with the vena mandibularis externa, the other with the 
vena jugularis interna. From this point the vein continues caudad on 
the dorsal aspect of the mandible to join the vena mandibularis externa 
behind the tympanic cavity. 
In Agama the sinus articularis hes dorsal to the trough-shaped 
mandible. It is connected with the vena mandibularis externa by two 
anastomoses, one of which passes through the foramen articulare, while 
the other runs above the lateral margin of the mandible. From a median 
direction the sinus also receives a short vein which takes its origin near 
the sinus prooticus; it corresponds to: the peripheral part of the vein 
which connects the sinus prooticus and the sinus articularis in Cnemido- 
phorus. In front of the articulation the vena mandibularis interna of 
Agama divides into two parts, one of which runs through the mandible 
below the articulation, while the other, larger division runs along the 
median side of the mandible. Behind the articulation the two veins 
unite and the trunk vein is connected anastomotically with the vena 
mandibularis externa, as in Cnemidophorus. In Agama a pretympanic 
connection between the vena mandibularis interna and the vena jugularis 
interna is wanting, but the vena tympanica anterior is represented by a 
short vein which drains the anterior wall of the tympanum.  Proceed- 
ing caudalward, the vena mandibularis interna runs between the floor of 
the tympanum and the mandible and joins the vena mandibularis ex- 
terna as in Cnemidophorus. 
From the foregoing accounts it seems probable that the posterior pro- 
longation of the vena fandibularis interna, as we find it in Agama and 
Cnemidophorus, is a primitive condition which has been modified in 
Lacerta by obliteration of the caudal part of the vein. 
2. VENA MANDIBULARIS EXTERNA (v. m. e., Text Figs. 2 and 3).— 
This vein begins near the symphysis of the jaw and runs caudad on the 
lateral aspect of the mandible until it reaches the level of the anterior 
wall of the tympanum. Here the vein enters the fold which forms the 
lower boundary of the external auditory depression, behind which it 
bends mesad and joins the vena mandibularis interna on the dorsal side 
of the articular bone. 
The chief tributaries and anastomoses of the internal and external 
mandibular veins are the following: 
(1) Sinus Dentalis (s. d., Text Fig. 3).—This sinus lies in the sub- 
mucosa internal to the dental furrow; it begins near the symphysis and 
