104 
MAMMALIAN ANATOMY 
the process, since if the process is unduly prolonged the injection 
mass will harden either in the cannula or the blood vessels. 
Moreover, a previous injection may at any time be supplemented 
by an application of warm water to melt it, and then injecting 
more of the mass at any desired point. When an injection is 
completed, the cannula is withdrawn, the escape of the mass 
prevented by a ligature around the vessel, or by an artery clamp, 
or simply by pressure from the fingers or a wad of wet cotton, 
while the specimen is held under a stream of cold water until the 
injection mass is hardened. 
To prepare the specimen for injection, lay back the skin from 
the ventral surface of the neck, trunk, and proximal region of the 
legs; open into the thoracic cavity by a longitudinal incision 
through the series of costal cartilages on each side of the sternum. 
Tie a ligature tightly around the sternum near its anterior end to 
prevent the escape of blood (and later of the injection mass) from 
the cut ends of the sternal veins and arteries. Sever the sternum 
transversely posterior to the ligature and, after freeing the pos¬ 
terior end from the diaphragm, remove it together with the stumps 
of the costal cartilages and thus expose the heart within the peri¬ 
cardium, in situ in the thoracic cavity. Carefully slit open the 
pericardium. From your previous study of the organ its parts 
may be readily identified. 
Open the abdominal cavity by a longitudinal incision a little 
to one side of the midline. Plug the rectum with cotton inserted 
through the anal opening, to prevent the escape of faecal matter 
(especially necessary in case the animal used is a cat). 
Identify by reference to the list given below, the various blood 
vessels through which the injections are to be made, and, where 
indicated, pass a ligature of coarse thread or fine cotton string 
about the vessel and tie the ends loosely in a single knot, laying 
them carefully out, one on each side so that they may be con¬ 
veniently drawn up tightly before the cannula is finally removed. 
i. Systemic Veins and Pulmonary Arteries with Blue. 
In case the animal is as large as an adult cat or rabbit, this 
injection may conveniently be made through the femoral vein 
which may be readily exposed upon either side in the angle between 
