io6 
MAMMALIAN ANATOMY 
remove the contents under a stream of water. In case the animal 
is a rodent, e.g., rabbit, white rat, or guinea pig, ligate the large 
intestine near the entrance into it of the caecum, make an incision 
at each end of the caecum and, after introducing a tube from a 
cold-water faucet into one of the incisions, turn on the water 
gently to wash out the contents of the caecum. In case the animal 
used is a cat, the large intestine should be emptied by a similar 
method. This process, though somewhat unpleasant, obviates 
greater inconvenience later. The specimen may be kept on ice 
in moist wrappings, or in running cold water for two or three 
days, but if it is desired to work on it longer, it should be skinned 
and preserved in 5% formalin, followed as usual by thorough 
washing in water before using. 
Directions for Dissection. —In general, dissection consists in 
removing the connective tissue which surrounds the blood vessels 
and holds them to adjoining structures, and by this means follow¬ 
ing out the vessel and its branches to the organs or regions which 
they supply. As the main veins and arteries follow the same 
general course, it will often be necessary to follow them out in a 
given region simultaneously. In no case should a blood vessel 
be cut until its connections have been fully determined and 
recorded. 
The record of the dissection must be kept in the form of a diagram 
{or a series of diagrams) which may either combine both the venous 
and arterial systems, or, if showing the two systems separately, 
should indicate correctly their anatomical relationships. The 
direction of blood flow should be indicated by arrows , and colors 
{corresponding to those used in injecting ) may be used to distinguish 
the different systems. 
The most convenient order to take in dissecting is as follows: 
1. The anterior vena cava 1 and its branches, working anteriorly 
from the heart, first very carefully laying open the narrow anterior 
end of the thoracic cavity by cutting through the attachments of 
the first pair of ribs to the sternum. 
2. The anterior branches of the aorta which issue from the 
thoracic cavity just dorsal to the anterior vena cava. 
1 In certain primitive mammals, e.g., the rabbit, there are two anterior venae cavae, 
a right and a left. 
