24 The Cephalic Veins and Sinuses of Reptiles 
foramen magnum and diverge from the median line, each vein bending 
directly laterad on its own side to reach the vena jugularis interna, 
which it enters from a dorsal direction. 
As it issues from the skull the vena cerebralis posterior gives rise to a 
vena spinalis (v. sp., Text Fig. 2), an intradural vein of small size, 
which runs along the lateral aspect of the spinal cord and receives inter- 
vertebral tributaries from the muscles which adjoin its path. Accord- 
ing to the observations of Corti, 41, on Psammosaurus, the vena spinalis 
discharges into the vena cava posterior. 
The only important feeder of the vena cerebralis posterior is the vena 
longitudinalis cerebri. 
Vena Longitudinalis Cerebri (v. 1. c., Text Fig. 2).—This is an intra- 
dural vein which extends from the olfactory lobes to the foramen magnum. 
In the adult lizard it is a small vein until it reaches the epiphysis, where 
it receives the epiphysial veins, which enter a ring formed by the vena 
longitudinalis cerebri around the distal end of the epiphysial stalk. The 
enlarged posterior part of the vena longitudinalis cerebri gives rise to 
the vena cerebralis media and to the vena cerebralis posterior, as already 
described. 
The vene epiphyseos have their roots in the cerebrum, where they 
drain the plexus chorioideus lateralis of the lateral ventricles. From 
each ventricle a single vein passes through the foramen Monroi and 
unites with its fellow in the roof of the third ventricle. The trunk 
vein ascends the stalk of the epiphysis, giving rise at the same time to a 
number of anastomosing branches, which form the plexus chorioideus 
anterior. From this plexus several small veins enter the ring of the 
vena longitudinalis cerebri. 
g. VENA JUGULARIS EXTERNA. 
(v. 7. e., Text Figs. 2 and 3.) 
The vena jugularis externa is a vein of medium size which extends 
from the vena mandibularis externa to the posterior end of the vena 
jugularis interna. The vein begins laterad of the articulation of the 
jaw, in a venous ring which gives rise to the vena communicans posterior. 
From its origin the vena jugularis externa runs through the cutaneous 
fold which forms the ventral margin of the external auditory depression ; 
it then takes a direction toward the shoulder joint, in front of which it 
bends mesad, penetrates the superficial muscles (cucullaris and episterno- 
cleido-mastoideus) and finally enters the vena jugularis interna near the 
