514 SPECIAL PHYSIOLOGY. 



death, and even when the intestine is removed from the body. By 

 narrowing the small intestine, they urge gently onwards, from its 

 upper to its lower end, the pulpy mixture of the alimentary substances 

 and digestive juices, gently compressing these soft materials against 

 the mucous membrane, passing them on, over the numerous valvulse 

 conniventes, and so undoubtedly aiding in absorption. The progres- 

 sive contractions of the longitudinal fibres open and unfold the coils 

 of the intestine, which otherwise might arrest the progress of its 

 contents. 



The peristaltic movements of the intestines are influenced, both 

 through the cerebro-spinal and sympathetic nervous systems ; this is 

 shown by experiments on animals, by irritation of the solar plexus, 

 spinal cord, and brain, and also by the peculiar effects of emotions on 

 these movements ; they are accelerated by moderate stimulation, and 

 retarded or arrested or inhibited, by more powerful irritations. But, 

 as they may continue after the intestine is removed from the body, it 

 is possible that they are usually excited, either by the direct stimula- 

 tion of the muscular fibres, or else, in a reflex manner, through the 

 intervention of the minute nervous ganglia found in the submucous 

 tissue, and in the circular and longitudinal muscular layers. The 

 stimuli which excite these motions are, in either case, the digested 

 food, and the various digestive fluids ; of the latter, the bile is the 

 most stimulating, and its importance as a regulator of the action of 

 the alimentary canal, is well known. 



Besides these intrinsic movements, the small intestine is acted upon 

 jointly by the diaphragm and the abdominal muscles, which subject 

 it to various degrees of pressure, and more or less alter its general 

 position in the abdomen; such movements must aid in urging on- 

 wards the contents of the intestine. It has been estimated that the 

 time occupied in the descent of the digested food along the small in- 

 testine is about three hours. 



The large intestine, Fig. 89, c to r, extends from the small intes- 

 tine to the termination of the alimentary canal. It measures usually 

 about five or six feet, i. e., about one-fifth of the whole length of the 

 intestinal canal. Though much shorter than the small intestine, it is 

 considerably wider, measuring from 1J to 2J inches in width, being 

 widest at its commencement, and gradually narrowing as it descends. 

 It pursues a remarkable course : commencing in the right iliac fossa, 

 where the small intestine opens into it, it ascends along the right side 

 to the under surface of the liver, then passes across between the um- 

 bilicus and the pit of the stomach, to the left side of the abdomen, 

 whence it descends to the left iliac fossa, and, having described a 

 double or sigmoid curve, enters the pelvis, through which it passes 

 down, supported by the sacrum and coccyx. The large intestine is 

 more or less arbitrarily divided into three parts ; the first part named 

 the ccecum, c, with its vermiform appendix ; the second part, the colon, 

 co to co, again subdivided into the ascending, transverse, descending 

 colon, and sigmoid flexure of the colon ; and the third part, or terminal 

 portion, named the rectum, r. 



The ilcum, t, enters the inner or left side of the large intestine, c, a 



