DISSECTION OF A EAT. 87 



INTERNAL. 



Cut the skin along the ventral median line from near the 

 vent to a point behind the jaw. Lay the skin back, separat- 

 ing the loose connective tissue which binds it to the deeper 

 parts. See the thin muscles covering the abdomen. Feel 

 for breast-bone, and open up the body by cutting through 

 muscular walls from between hind-legs to breast-bone. 

 Make transverse cuts on either side, and fold the walls out- 

 wards. This opens the peritoneal cavity. In this, with- 

 out disturbing parts, can now be seen, in front, the dark- 

 colored liver, behind this the coils of the intestine, and be- 

 tween the hinder coils of this tube the urinary bladder. 



Tip the liver to your left and find the stomach. Sketch 

 from the side, showing the entrance of the gullet (oesophagus) 

 and the beginning of the intestine. Notice how liver and 

 stomach are connected by thin membrane (mesentery). 

 Tip the stomach forward and notice the spleen suspended 

 in another portion of the mesentery. 



Trace the intestine, without cutting anything. It is also 

 held by its mesentery. It makes first a large loop back- 

 wards (duodenum) and then comes forward to form numer- 

 ous convolutions. Find a largo pocket (caecum) given off 

 from the intestine. All of the tube in front of this is 

 called the small intestine; back of it the large intestine. 

 In the latter two portions (1) colon, (2) rectum can 

 readily be distinguished by the different appearance of the 

 walls. 



Spread out a portion of the mesentery supporting the in- 

 testine and notice in it small vessels. Some of these will 

 be found to be single, others double. The double vessels 

 are arteries and veins. They can be distinguished by trac- 

 ing them towards the middle line of the body. The veins 



