52 ANATOMY OF THE RAT 



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, exer- 

 cising great care to remove nothing but the skin. Do not 

 remove the integument between the hind legs on the ven- 

 tral and posterior surfaces until ready to study the urino- 

 genital 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 dia- 

 phragm 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 scis- 

 sors 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 pul- 

 monary 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. 



