--For this purpose a
half-grown cat is generally the best available material. This should be
killed with chloroform and secured to a board as in the dissection of the
abdomen (page 169). Open the abdominal cavity and remove the contents,
tying the alimentary canal where it is cut, and washing out any blood
which may escape. Dissect for the nervous system in the following order:
1. Cut away the front of the chest, exposing the heart and lungs. Find on
each side of the heart a nerve which passes by the side of the pericardium
to the diaphragm. These nerves assist in controlling respiration and are
called the _phrenic_ nerves. Find other nerves going to different parts of
the thorax.
2. Remove the heart and lungs. Find in the back part of the thoracic
cavity, on each side of the spinal column, a number of small "knots" of
nervous matter joined together by a single nerve. These are sympathetic
ganglia. Where the neck joins the thorax, find two sympathetic ganglia
much larger than the others.
3. Cut away the skin from the shoulder and upper side of the fore leg. By
separating the muscles and connective tissue where the leg joins the
thorax, find several nerves of considerable size. These connect with each
other, forming a network called the _brachial plexus_.
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