PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 287 



the thin abdominal walls, even while the cavity is unopened. According to Schiff, the 

 only cause of these exaggerated movements is diminution or arrest of the circulation. 

 This physiologist, by compressing the abdominal aorta in a living animal, was able to ex- 

 cite peristaltic movements in the intestine as vigorous as those which take place after 

 death ; and, on ceasing the compression, the movements were arrested. 



The nerves distributed to the small intestine are derived from the sympathetic, and 

 from branches of the pneumogastric, which latter come from the nerve of the right side 

 and are distributed to the whole of the tract, from the pylorus to the ileo-cgecal valve. 

 The intestine receives no filaments from the left pneumogastric. The experiments of 

 Brachet, by which he attempted to prove that the movements of the intestines were 

 under the control of the pneumogastric and nerves emanating from the spinal cord, have 

 not been verified by other observers. Eecent experiments render it probable that an 

 influence, derived from the cerebro-spinal system, is essential to the functions of the 

 sympathetic ganglia, which may account for some of the results obtained by Brachet 

 after dividing the spinal cord. The experiments of Mtiller, however, render it certain 

 that the peristaltic movements are to some extent under the influence of the sympathetic 

 system. In these experiments, movements of the intestine were produced by galvaniza- 

 tion of filaments of the sympathetic distributed to its muscular coat, after the ordinary 

 post-mortem movements had ceased. The same results followed the application of caustic 

 potash to the semilunar ganglia, the movements reappearing when the potash was applied, 

 " with extraordinary vivacity " in the rabbit, after the abdomen had been opened and the 

 movements had entirely ceased. These experiments have been confirmed by Longet, 

 who found, however, that the movements did not take place unless alimentary matters 

 were contained in the intestine. 



It must be acknowledged that very little is known concerning the reflex actions which 

 take place through the sympathetic system ; but there is certainly good ground for sup- 

 posing that certain reflex functions are performed by this system of nerves, one of the 

 most important of which is the production of peristaltic movements in obedience to the 

 impression made by alimentary substances upon the mucous membrane. This impression 

 is probably conveyed to the semilunar ganglia and reflected back through the motor nerves 

 to the muscular coat of the intestine. 



Physiological Anatomy of the Large Intestine. 



The large intestine, so called because its diameter is greater than that of the rest of 

 the intestinal tract, receives for the most part only the indigestible residue of the food, 

 mingled with certain of the secretions which are discharged into the small intestine. In 

 the human subject, the processes of digestion which take place in this part of the ali- 

 mentary canal are unimportant ; and it is probable that, under physiological conditions, 

 hardly any thing but water is absorbed by its lining membrane. Matters are, however, 

 stored up in the large intestine for a number of hours, and a certain amount of secretion 

 takes place from its follicular glands. 



The entire length of the large intestine is from four to six feet. Its diameter is great- 

 est at its commencement, where it measures, when moderately distended, from two and a 

 half to three and a half inches. According to the observations of Brinton, the average 

 diameter of the tube beyond the caBCum is from one and two-thirds to two and two- 

 thirds inches. Passing from the caecum, the canal diminishes in caliber, gradually and 

 very slightly, to where the sigmoid flexure opens into the rectum. This is the narrowest 

 portion of the canal. Beyond this, the rectum gradually increases in diameter, forming 

 a kind of pouch, which abruptly diminishes in size near the external opening, to form the 

 anus. 



The general direction of the large intestine is from the coBcum in the right iliac fossa 

 to the left iliac fossa, thus encircling the convoluted mass formed by the small in- 



