8 The Cephalic Veins and Sinuses of Reptiles 
vessel, diverges from the middle hne and makes its way, through a notch 
in the basisphenoid bone, to the lateral aspect of the Eustachian furrow, 
along which it ascends toward the roof of the tympanic cavity. Directly 
anterior to the tympanum the vein receives a large anastomotic vessel 
from the lower jaw, the vena tympanica anterior, after which it passes 
between the quadrate bone and the ear capsule and enters the roof of 
the tympanum. Here the vena jugularis interna runs on the dorsal side 
of the ramus posterior facialis* (r. p. f., Text Figs. 2 and 7). Continu- 
ing caudad the vein passes between the posterior end of the parotic pro- 
cess and the cranial end of the second epibranchial cartilage of Parker, 
84, the latter of which lies between the vein and the trunks of the pos- 
terior cranial nerves (1X, X, XI, Fig. 3, Plate I). Here the vena 
jugularis interna receives the vena mandibularis, which approaches the 
trunk vein from a lateral direction (v. m., Text Figs. 2 and 3). Close 
behind the junction of these veins the vena cerebralis posterior passes 
over the epibranchial cartilage from a medial direction and enters the 
jugular vein from above. In this region the vena jugularis interna is 
surrounded by a small muscle, m. constrictor vene jugularis interna, 
which is described in the second part of this paper. 
Behind the junction of the vena mandibularis with the jugular vein 
the cranial nerves which lie on the median side of the epibranchial carti- 
lage begin to separate, the vagus following the jugular vein, the glos- 
sopharyngeus and hypoglossus running below the vein, as described by 
Grosser and Brezina. The trunk of the accessorius, on the other hand, 
passes above the jugular vein to reach its peripheral territory, the m. 
cucullaris and m. episterno-cleido-mastoideus. This nerve, therefore, 
forms an exception to the rule that the post-trigeminal nerve trunks of 
the adult Lacerta agilis lie ventral or medial to the vena jugularis 
interna. 
In the neck region the vena jugularis interna runs on the median side 
of the m. episterno-cleido-mastoideus, where it lies close td the vagus and 
the carotid artery. Approaching the heart the vein receives the vena 
jugularis externa then bends mesad to discharge into the vena cava 
anterior. 
1In Platydactylus the vena jugularis interna shows a tendency to retain 
its primitive relation to this nerve and to the chorda tympani, the latter of 
which becomes an independent nerve near the level of the ganglion facialis. 
In two specimens examined the chorda tympani passes above the vein. In 
one of these the ramus posterior facialis takes a similar course. 
In a specimen of Anguis fragilis the vein lies below the auditory nerve 
but above the ramus posterior facialis. 
