90 ELEMENTS OF COMPARATIVE ZOOLOGY. 



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 projects from the outer wall a papilla. 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 ventral 

 to the postcava, and continue the cut along the ventral sur- 

 face 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 ossophagus. These pass forward be- 

 tween the lobes of the lungs. Notice the thin membrane 

 (mediastinum) passing dorsally from the breast-bone to 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. 



Cut open the pericardium and study the heart. Its apex 

 is directed backward and to the (animal's) left ; its broader 

 base in front and to the right. Tip the heart to your right, 

 and notice how the postcava enters it near the base on the 

 right side. Just before its entrance into the heart it re- 

 ceives a similar vessel (the precava) from in front. Follow 

 the precava forward, cutting away the fatty-looking thymus 

 gland just in front of the heart in order to trace the vessel. 

 Soon it divides into right and left branches (jugulars) each 

 of which receives a vessel (subclavian vein) from the cor- 



