54 LABORATORY WORK. 



third eyelid at inner angle of the eye. Does it resemble 

 any structure you have found in the animals previously 

 studied? Is there anything similar in your own eye? 



INTERNAL. 



Cut the skin along the ventral median line from near 

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

 separating the loose connective tissue which binds it to the 

 deeper parts. See the thin muscles covering the abdo- 

 men. Do they show any signs of segmental repetition? 

 (cf. Frog). Feel for the 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 outwards. This opens the perito- 

 neal cavity. In this, without disturbing parts, can now 

 be seen, in front, the dark-colored liver, behind this the 

 coils of the intestine, and between 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 (oesopha- 

 gus) 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 large pocket (ccecum) 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. 



