DIGESTIVE SYSTEM 215 



3. The stomaeli is U-shaped. Its proximal Umb, which is 



very wide and directly continuous with the cesophagus, 

 extends back nearly, to the hinder end of the abdo- 

 minal cavity : it then turns sharply forwards to 

 form the distal limb, which is shorter and much 

 narrower. 



4. The intestine is separated from the distal limb of the 



stomach by a sUght pyloric thickening. Its proximal 

 part is about equal in width to the stomach, alongside 

 which it Ues ; but it soon dilates to form the wide 

 colon, the surface of which is marked spirally by 

 blood-vessels, corresponding to the line of attachment 

 of the spiral valve. At its hinder end the intestine 

 narrows to form the rectum which, after a course 

 of about an inch and a half, opens to the exterior at 

 the cloacal aperture. 



a. The spiral valve. 



Open the intestine along its whole length by a longitudAnal 

 incision along its right side. Wash out its contents. Carefully 

 cut OAJBay with scissors the ventral wall from the several turns 

 of the spiral valve, and turn it over to the left side, so as to 

 fully expose the cavity of the intestine. Wash freely. 



The spiral valve is a membranous fold, attached 

 along one edge to the inner surface of the intes- 

 tine, round which it runs spirally. The fold is 

 about an inch and a half wide at the anterior 

 end, but gradually diminishes in width towards 

 the posterior end, and disappears at the com- 

 mencement of the rectum. The first turn of the 

 spiral is a long one, but the succeeding ones, of 

 which there are usually seven or eight, are only 

 about a quarter of an inch apart. The general 

 appearance of the valve is that of a series of cones 

 one within another, the apices of the cones being 

 usually directed forwards, but sometimes at the 

 hinder end backwards. 



