690 



Journal of Agriculture. 



[8 Nov., 1907. 



At the same time the longitudinal coat helps by contracting, so that the 

 gut wall is pulled over the food-mass. This worm-like action is called 

 ■peristalsis. Peristalsis is raoid in the oesophagus but slow in other 

 regions of the canal. In the oesophagus and in the first part of the colon 

 of most mammals peristalsis can also take place in the reverse direction,, 

 nameU , towards the mouth. 



Another movement that is found in many parts of the canal is a 

 peristalsis of a xery weak character, the constriction of the tube being 

 never complete. This mo\"ement does not urge the entire food mass- 

 onwards ; it seems rather to drive forward the most outward layer of 

 the food and to bring a fresh surface in contact with the mucous membrane. 



\'illi. Intestinal ulands. 



Sulmmcosa. 



Fi^'. 46. 



Musculari.s 



Transverse section of a patch of Peyer of the small intestine of a cat. 

 The crests of four nodules were not within the plane of the section. (After 

 Stohr.) 



Dilated parts of the canal like the crop, caecum, colon and fundus 

 of stomach do not show a true peristalsis. On their walls faint wa\es 

 of muscular contraction may be seen which produce surface currents in 

 the food-mass or rotate the whole. These organs are also' capable of 

 strong contraction involving the whole wall so that the contents can be 

 squeezed out. 



When a thin part of the canal opens into or out of a dilated part 

 we generally find a strong ring of circularly disposed smooth muscle, 

 really an enlargement of the ordinary circular layer, which maintains 

 a continued contraction and keeps the entrance or exit of the dilated part 

 closed. This muscular ring only relaxes when it is necessary for a 

 food-mass to be dri\-en through and wlien this is o\er the ring closes up 

 tightly again. Such rings of muscle are called sphincters. The 



