Henry L. Bruner 43 
striated muscle which surrounds the jugular vein in the region where the 
latter passes from the head into the neck. In its simpler form the muscle 
has a single attachment to the skeletal parts, a portion of its fibers aris- 
ing from the parotic process* directly lateral to the vein. This form of 
the constrictor muscle occurs in Phrynosoma and Monitor. 
In Phrynosoma cornutum the constrictor muscle (Text Fig. 5) en- 
velopes the vena jugularis interna for a distance of about 1600 p. The 
attachment of the muscle begins about 400 » behind the anterior end 
V2. 
Fic. 5. M. constrictor venze jugularis interne of Phrynosoma cornutum, 
left side, from above. xX 32. 
The general relations were obtained by reconstruction. The muscle fibers 
are drawn to seale but their arrangement is somewhat diagrammatic. 
P., part of the parotic process; v. j. i7., vena jugularis interna; v. c. p., vena 
cerebralis posterior. 
and continues caudad 450 p. Opposite from the attachment of the 
muscle the vena cerebralis posterior (v. c. p.) penetrates the muscle to 
reach the jugular vein (compare also Figs. 1 and 2, Plate I). 
The fibers of the muscle spring from the posterior descending part 
of the parotic process, partly from the occipitale laterale (Ol., Fig. 2, 
Plate I), partly from a remnant of cartilage which les between the 
*This is the parotic process of Parker, 84, p. 140, which is formed in the 
adult chiefly by the occipitale laterale and the opisthoticum. In the embryo 
it is composed of cartilage, some of which may persist in the adult. 
