Henry L. Bruner 29 
from a prolongation of the sinus which accompanies the lachrymal 
gland caudad from the orbit. The vein emerges from the capsule of the 
gland opposite the anterior end of the prootic bone, where also it receives 
a musculo-cutaneous tributary from the dorsal region of the head. From 
the junction of the two veins the vena jugularis interna runs directly 
caudad, following a course which lies close to the cranial wall and above 
the roots of the trigeminus and the more posterior cranial nerves. In 
the anterior part of its course the vein is connected by one or more anasto- 
moses with the posterior prolongation of the sinus orbitalis. Farther 
caudad it receives two large tributaries from the cranial cavity: the vena 
cerebralis media, which passes through the foramen for the second and 
third branches of the trigeminus, and the vena cerebralis posterior, which 
leaves the skull by way of the foramen magnum. Beyond the terminus 
of the latter vein the vena jugularis interna descends to the side of the 
cesophagus, where it receives the vena mandibularis, the vena cesophagea, 
and the vena cervicalis lateralis. The mandibular vein is described 
below. The vena cesophagea drains the cesophagus and the deeper muscles, 
the vena cervicalis lateralis (v. c. J., Text Fig. 4) receives blood from 
the skin and superficial muscles of the neck. These two veins enter the 
vena jugularis interna at about the same level directly behind the mouth 
of the vena mandibularis. In Text Fig. 4 the mouth of the vena ceso- 
phagea is concealed by the vena jugularis interna. 
In this region the jugular vein is enveloped by a small striated muscle, 
m. constrictor vene jugularis interne, which also surrounds the terminal 
parts of the vena mandibularis, vena cervicalis lateralis, and vena ceso- 
phagea. ‘The muscle is described in the second part of this paper. 
The following tributaries of the vena jugularis interna require a more 
detailed description : 
(a) Sinus orbitalis, (b) vena cerebralis media, (c) vena mandibularis. 
a. THE SINUS ORBITALIS. 
(s. o., Text Figs. 1 and 4.) 
The sinus orbitalis of the snake is somewhat reduced on account of the 
absence of movable eyelids; it occupies, however, all of the deeper part 
of the orbit and reaches laterad somewhat beyond the equator of the bul- 
bus. Anteriorly the sinus extends to the opening of the naso-lachrymal 
duct; posteriorly it follows the lachrymal gland between the cranial wall 
and the skin and gives rise to the vena jugularis interna. 
The sinus orbitalis is drained largely, perhaps chiefly, by the vena 
