_Preparation and Injection._--A new specimen must be prepared for the
dissection of the blood-vessels. The same specimen may be used, if
necessary, for the dissection of the peripheral nervous system,--one
side being used for the blood-vessels, the other for the nerves,--but it
is much better to use separate specimens for the two systems.
Inject the femoral artery of the specimen with either five per cent.
formalin, or with the mixture of five per cent. formalin and glycerine,
exactly as for the muscles. Then, without removing the canula or
waiting, inject the artery with red starch. This is prepared as follows:
Mix together equal volumes of vermilion (or red lead), glycerine, and
five per cent. formalin. Grind these together in a mortar, so as to
destroy the lumps; strain the resulting mixture through fine muslin.
This color mixture can be preserved in a closed bottle till it is to be
used. Then mix together one volume of dry starch, one and one-fourth
volumes of five per cent. formalin, and one-fourth volume of the color
mixture. See that no lumps are present.
Inject the above red starch mass into the femoral artery. It will drive
into the veins the formalin already injected, and the arteries will be
filled with the red starch.
The veins need not be injected, as they will be found to be filled with
the formalin mixture, colored by the blood, so that they can be traced
without great difficulty.
_Dissection of Blood-vessels._--In general the arteries and veins will
be traced together. It is an excellent plan to make a sketch of each
vessel as it is dissected, showing its origin, branches, and name. This
will be a great aid to the memory and will be of much assistance in
reviewing the vessels. The sketches can later be combined into a
well-ordered drawing. The description of each vessel must of course be
studied as the vessel is dissected.
In tracing blood-vessels _do not_ grasp them between the forceps-blades,
but handle them by taking hold with the forceps of the connective-tissue
coats of the vessels. _Do not_ use the scalpel, but _pull_ away the
connective tissue and fat with fine forceps, using two pairs of forceps
or one forceps and the tracer.
Variations are especially common in the blood-vessels, and the student
must not be surprised to find considerable deviations from the
conditions described and figured in the text. These variations usually
present nothing new in principle and are easily understood by comparing
them with the structures described.
_Directions for Dissecting the Blood-vessels._--Make a median
longitudinal incision through the skin from the symphysis of the jaw to
the caudal end of the xiphoid process. About three or four centimeters
caudad of the cranial end of the sternum make an incision at nearly
right angles to this, passing from the first incision on the ventral
side of the left arm about to the elbow. Reflect the flaps of skin, so
as to uncover the left side of the thorax and the under surface of the
arm, exposing the pectoral muscles. Isolate and transect the pectoral
muscles one at a time, cutting each near its thoracic attachment. (The
muscles (p. 145) should be reviewed at the same time.) In this way the
nerves and blood-vessels of the axilla are exposed (Fig. 122, p. 295).
Find the axillary artery and vein (Fig. 122, _f_ and _g_) emerging from
the thorax just craniad of the first rib, along with the nerves of the
brachial plexus. Remove connective tissue, etc., so that the vessels and
nerves are well isolated as they pass out of the thorax. Take great
pains not to puncture the vessels, particularly the veins.
Then remove the left side of the thorax by cutting through the first rib
near its sternal end and then near its dorsal end, without injury to the
vessels and nerves, cut the other ribs in the same way, and take out the
thoracic wall.
Now find with tracer and forceps the great blood-vessels leaving the
cranial end of the heart (see Fig. 118). Take the greatest pains not to
injure them. Find the aorta and aortic arch (p. 281); the left
subclavian artery (p. 283) (continuous with the axillary); the
innominate artery (p. 282), and the beginnings of its three branches
(see Fig. 115). Find also the superior vena cava, the innominate veins,
and the subclavian vein, continuous with the axillary vein.
I. Study the smaller branches of the thoracic aorta (p. 283, and Fig.
118)--the intercostals, the bronchial and œsophageal arteries, and the
first pair of lumbar arteries. (The coronary arteries will be examined
later.)