blood out of the arteries, through the capillaries and into the veins, which will therefore be filled, after preservation, with dark coagulated blood. The fluid may be introduced through the left ventricle of the heart.
VEINS ANTERIOR TO THE HEART
Skin a rat whose blood vessels have been injected, exercising great care to remove nothing but the skin. Do not remove the integument between the hind legs on the ventral and posterior surfaces until ready to study the urinogenital system. Place the skinned animal upon its back and slit the thorax along a line parallel to the sternum but seven or eight millimeters to its left, and extending from the diaphragm to the level of the anterior end of the heart. Continue the incision dorsally along the junction of diaphragm and body wall. Expose the thoracic cavity by pressing this flap outward. The lungs and heart will be seen through this aperture. The membranous attachments of the lungs will not be injured by this dissection if the scissors are not thrust too far into the thoracic cavity. Avoid extending the incision too far forward, as the blood vessels anterior to the heart region will be cut.
Observe the membranous sac (pericardium) surrounding the heart, the large organ in the middle of the cavity. Note the mesentery-like mediastinal septum extending from the diaphragm to the anterior end of the thoracic cavity, and from the pericardium to the sternum. The small pulmonary lobe just behind the heart lies loosely in a chamber inclosed by the diaphragm behind, by lateral membranes extending from the pericardium to the diaphragm, and in front by the pericardium. The large left lobe of the lung is attached by a membrane along its dorsal border to the esophagus, or to the membrane inclosing the pulmonary lobe mentioned above.
