THE CAT 211 



of a nail or strong pin, or a cord. Make an incision through the 

 skin in the midventral line the entire length of the body. Separate 

 the skin from the fat and muscles beneath it for a short distance 

 on each side of the incision. Make now a midventral incision 

 through the body wall from the pelvic girdle, which may be felt 

 through the muscles at the hinder end of the trunk, to the breast- 

 bone, which may be felt a short distance back of the forelegs ; 

 make also a short transverse cut on each side, from the middle of 

 this incision. 



The cavity of the abdomen will thus be opened. The red lobes 

 of the liver, the green gall bladder, and the stomach will be 

 seen at the forward end of this cavity, the stomach lying at the 

 left of the liver. Back of these organs is an extensive membrane, 

 the fat-filled great omentum, covering the intestine. At the hinder 

 end of the cavity will be seen the urinary bladder, which is joined 

 with the ventral body wall by a thin mesentery. The forward ends 

 of the stomach and liver rest against a transverse muscular parti- 

 tion, the diaphragm, which forms the forward wall of the ab- 

 dominal cavity. 



Make now with scissors a longitudinal incision along each side 

 of the breastbone through the body wall to the forward end of 

 the trunk. Cut the diaphragm where it joins the ventral body 

 wall on each side. Lift up the hinder end of the breastbone and, 

 without further cutting or disturbing anything, look into the 

 thoracic cavity, which is thus opened. 



It will be seen, in the first place, that the entire body cavity 

 is made up of these two divisions, the abdominal cavity and the 

 thoracic cavity, which are separated by the diaphragm. 



The thoracic cavity contains the lungs, the heart and the great 

 vessels which enter and leave it, the posterior portion of the 

 cesophagus and the trachea, and .the thymus. A thin membrane 

 called the pleura lines its inner surface. The space within the 

 thorax is not, however, a continuous one, but is subdivided into 

 several distinct compartments. The pleura forms two closed sacs, 

 called the pleural sacs, which occupy the right and left sides of 

 the thoracic cavity. Within each of these sacs one of the lungs 

 projects, covered by a fold of the pleura. 



