Mammalia. 



129 



When the chest is first opened, look in to see the position of 

 the heart. The attachment along the inside of the breastbone 

 must be cut close to the bone. 



When the breastbone is reached, let the cut fork to each side 

 along the line where the bony part of the ribs ends and the 

 cartilaginous part begins. At the anterior end cut across the 

 breastbone and entirely remove it. Extend the slit in the .ab- 

 dominal wall to the pelvis. Make slits outward in the middle 

 of each side of the abdominal wall ; turn the flaps outward, pin- 

 ning them down if necessary. There are now disclosed the two 

 parts of the body cavity, the chest cavity, or thoracic cavity, 

 containing the heart and lungs, and the abdominal cavity, con- 

 taining the digestive organs. Between these two cavities, and 

 the sole partition separating them, is the thin muscular dia- 

 phragm. Examine the diaphragm from the anterior side. Can 

 you see that its central part is thin and nearly transparent? 

 This is the tendinous part of the diaphragm. Note the shape 

 of the diaphragm as seen from the front. Gently press the liver 

 backward to see the posterior surface of the diaphragm. Take 

 hold of the diaphragm with thumb and finger on its opposite 

 surfaces to learn its thinness, its smoothness and flexibility. Is 

 the diaphragm flat or arched ? How is it arched ? 



THE ORGANS OF THE ABDOMINAL CAVITY. 



1 . Observe that the ventral wall of the abdomen is composed 

 of muscle. Its smooth lining is the peritoneum. Feel of it. 



2. Study the abdominal organs in their natural position. 

 Filling most of the space of the abdominal cavity is the coiled 

 intestine ; next to the diaphragm is the dark-colored liver ; back 

 of the liver, and partly covered by it, is the stomach ; and in 

 the posterior part of the abdomen is the bladder. 



3. Pull the intestine backward, and make out the shape, size, 

 position, and color of the stomach. Observe how the liver and 

 stomach fit together ; push the liver forward, and turn the 

 stomach back to find a white tube entering its anterior surface ; 



