oe) 
8 The Cephalic Veins and Sinuses of Reptiles 
another specimen (Text Fig. 12) the vein is dilated, its walls are thin 
and the muscle fibers are slender and more loosely arranged. 
The m. constrictor ven jugularis interne has been observed in the 
European Ringelnatter (Tropidonotus natriz), in the black snake of the 
United States (Zamenis constrictor), in the sea snake (Hydrophis 
Hardwickti, Text Fig. 14), in a rattlesnake (Crotalus adamanteus), and 
in a species of Helminthophis from Jamaica. In all of these the muscle 
shows practically the same relations and structure. 
Fic. 12. Transverse section through the region of the m. constrictor vene 
jugularis interne of Tropidonotus natrix, right side. Specimen 55 cm. long. 
pnb 0: 
The section passes behind the mouth of the vena mandibularis. 
ep., epithelium of pharynx; m. c. h., m. cervico-hyoideus; m. c. 7. 7., mM. con- 
contrictor vene jugularis interna (the vein is dilated and the muscle fibers 
are relaxed and slender); m. c. m., m. cervico-mandibularis (sphincter colli) ; 
vy. §., part of a ventral scale. 
In Tropidonotus the m. constrictor vene jugularis interne is inner- 
vated by two small nerves, nervi tumetfactores capitis, which arise from 
the vagus a short distance behind the inferior ganglion (ganglion trunci 
vagi of authors), where the vagus lies on the median side of the vena 
jugularis interna. One of these nerves enters the anterior border of the 
constrictor muscle above the jugular vein. The other nerve arises a 
