24 THE VASCULAR SYSTEM OF THE FROG. 
render the vein itself difficult to see owing to the loss of colour. 
Always dissect along and not across a bloodvessel, and pin out the 
parts so as to stretch vt slightly. 
I. Veins opening into the Sinus Venosus, 
a. The right superior vena cava: a large vein opening 
into the right side of the sinus venosus, and returning 
to it the blood from the right side of the head and 
body, and from the right fore-limb. It is formed by 
the union of three veins :— 
1. The external jugular vein: formed by 
i. The lingual vein: from the floor of the mouth 
and the tongue. 
ii. The mandibular vein: from the margin of 
the lower jaw. 
2. The innominate vein: formed by 
i. The internal jugular vein: returning blood 
from the interior of the skull, which it leaves 
by an aperture at the posterior border of 
the orbit. . 
ii. The subscapular vein: a small vein from the 
back of the arm and shoulder. 
3. The subclavian vein: the largest of the three: 
formed by 
i, The brachial vein: from the fore-limb. 
iii The musculo-cutaneous vein: a very large 
vein returning blood from the skin and 
muscles of the side and back of the body, 
and of the head as far forwards as the nose. 
are the same as those of the right. 
c. The inferior vena cava: a median vein which, com- 
mencing between the kidneys, runs forward to open 
into the posterior end of the sinus venosus. It returns: 
to the heart blood from the liver and from the kidneys, 
