Atwood—The Viceral Anatomy of the Garter Snake 537 
entering the anterior azygous vein just before it enters the rigth 
jugular vein. 
The azygous veins of different species of serpents differ greatly 
and in the writer ^s estimation might well be used in classification. 
The branches from the epigastric vein to the right jugular 
vein varied from three to seven in eighteen specimens examined. 
They averaged four. The epigastric vein in Thamnophis is more 
continuous in the neck region than in Zamenis constrictor (At¬ 
wood, T6), and has fewer connections with the right jugular 
vein. 
The esophageal vein of O’Donoghue (T2) could not be found 
in Thamnophis. 
The Left Jugular Vein. 
The left jugular vein originates in the head and courses along 
the left ventral surface of the esophagus to the heart. It passes 
ventral and to the left of the left atrium and traverses the dorsal 
surface of the heart, from left to right, between the left atrium 
and the ventricle to enter the right atrium through the sinus 
venosus together with the vena cava and the right jugular vein. 
It is nearly as large as the right jugular vein. 
FIG. 2. 
The right jugular vein. AZ, right azygous vein; E, esophageal veins; 
EV, epigastric vein; PZ, posterior azygous vein; RA, right atrium; RJ, 
right jugular vein; RT, right thymus gland; T, vein from tongue 
muscles; VC, vena cava^; T, branch from the ...epigastric vein to the left 
jugular. 
The first branch of the left jugular vein is received just be¬ 
fore it enters the pericardium of the heart near the anterior end 
of the left atrium. It carries blood from the esophagus and is 
the first of a series of veins, which differ in number, from the 
esophagus to the left jugular vein. This series begins in the 
region of the heart and extends throughout the length of the 
