448 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



to Valentin, 100 grammes of faeces of the bog contains 37.2 grammes, 

 ox 15.2 grammes, horse 13.3 grammes, sheep 13.5 grammes of ash: 



XIII. THE MOVEMENTS OF THE INTESTINES. 



The walls of both small and large intestines are supplied with un- 

 striped muscular fibres arranged in circular and longitudinal layers 

 which, through their contraction, serve to cause a slow, onward, pro- 

 gressive movement in the contents of the alimentary tube. 



The arrangement of these muscular fibres differs in the small and large 

 intestine and in different animals. The longitudinal layers lie beneath 

 the submucous layer immediatel}' below the serous covering, and, there- 

 fore, give the intestine its longitudinally Striated appearance. 



In the small intestine these longitudinal fibres form a thin, uniform 

 layer, which entirely surrounds the intestine, while in the large intestine 

 they are grouped into bands, and, being rather shorter than the intes- 

 tine, throw the intermediate parts into a series of pouches ; this con- 

 dition is seen in the large intestine of man, the omnivora, in the caecum 

 of solipedes, and in the fixed colon in these animals, while in the floating 

 colon their arrangement is more similar to that seen in the small intes- 

 tine, and, consequent^, in those portions of the alimentary tract the 

 sacculated appearance is wanting. Immediately below the longitudinal 

 fibres is found the layer of circular fibres, which are considerably more 

 developed than the longitudinal fibres. 



The motions of the intestine have been compared to the move- 

 ments of a worm, and are termed peristaltic contractions. When the 

 abdomen of an animal is opened after death the walls of the intestine 

 are seen to be in active motion, and cause the intestine thus to undergo 

 a series of active movements of the same nature, but greatly exaggerated 

 in intensity, as the movements occurring during life. If the intestines 

 are closely examined, it will be seen that these movements consist in the 

 downward passage of a constriction due to the successive contractions of 

 the circular fibres of the small intestine from above downward, while at 

 the same time the longitudinal fibres contract immediately below the 



