RAT. 57 



scissors into the postcava, make a cut. Continue this 

 until the whole vessel is laid open up to the diaphragm. 

 On the inner surface of the postcava, inside the liver, 

 notice the openings of the hepatic veins. These bring to the 

 postcava the blood which entered the liver by the portal 

 vein. 



Add these parts to the sketch of the blood system 

 already begun. 



With a sharp scalpel split a kidney horizontally. In the 

 cut section make out on the median side a cavity (the 

 pelvis of the kidney) from which arises the ureter. Into 

 the pelvis a papilla projects from the outer wall. In the 

 thick outer wall notice the difference in appearance 

 between the outer cortical substance and the more central 

 medullary substance. Sketch the cut section. 



Notice the direction of the muscle-fibres in the dia- 

 phragm. What would be the effect of their contraction 

 upon the diaphragm? * Cut through the diaphragm ven- 

 tral to the postcava and continue the cut forward along 

 the ventral surface of the body to one side of the median 

 line. Cut the ribs with stout scissors. This will lay open 

 the pleural cavity. 



In the pleural cavity, behind, will be seen the postcava, 

 and dorsal to it the oesophagus. These pass forward 

 between the lobes of the lungs. Notice the thin mem- 

 brane (mediastinum) passing dorsally from the breast- 

 bone towards the heart and lungs. The heart itself will 

 be found to be enclosed in its own thin sac (pericardium). 

 Sketch the contents of pleural cavity. 



* An instructive demonstration can be made by opening the 

 abdominal cavity of some small mammal in which the diaphragm 

 is so thin that the lungs are seen in outline through it. Then 

 puncture the diaphragm and note the effect on the lungs. 



