PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 257 



pathetic and from branches of the pneumogastric, which latter come from 

 the nerve of the right side and are distributed to the whole of the intestinal 

 tract, from the pylorus to the ileo-caecal valve. The intestine receives no 

 filaments from the left pneumogastric. Throughout the intestinal tract, is a 

 plexus of non-medullated nerve-fibres with groups of nerve-cells, lying be- 

 tween the longitudinal and circular layers of the muscular coat. This is 

 known as Auerbach's plexus. From this plexus, very fine, non-medullated 

 filaments are given off, which form a wider plexus, also with ganglionic cells, 

 situated just beneath the mucous membrane. This is called the plexus of 

 Meissner. 



The experiments of Brachet, by which he attempted to prove that the 

 movements of the intestines were under the control of the pneumogastrics 

 and nerves given off from the spinal cord, have not been verified by other 

 observers. The experiments of Mtiller, however, render it certain that the 

 peristaltic movements are to some extent under the influence of the sympa- 

 thetic system. In these experiments, movements of the intestine were pro- 

 duced by stimulation of filaments of the sympathetic distributed to its mus- 

 cular coat, after the ordinary post-mortem movements had ceased. The 

 same results followed the application of potassium hydrate to the semilunar 

 ganglia, the movements reappearing when the agent was applied, " with ex- 

 traordinary 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. 



The fact that movements occur in portions of intestine cut out of the 

 body and separated, of course, from the nervous system, has led to the view 

 that the peristaltic action is automatic, like the action of the excised heart, 

 and these automatic movements have been attributed to the influence of the 

 ganglia found in the intestinal walls. An analogy between such intestinal 

 movements and the movements of the excised heart seems probable ; and a 

 reasonable explanation of this action is afforded by the existence of ganglia 

 in the plexuses of Auerbach and of Meissner. 



PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE. 



The entire length of the large intestine is about five feet (1-5 metre.) Its 

 diameter is greatest at the caecum, where it measures, when moderately dis- 

 tended, two and a half to three and a half inches (6*35 to 8'89 cen- 

 .timetres). According to the observations of Brinton, the average diameter 

 of the tube beyond the caecum is one and two-thirds to two and two-thirds 

 inches (4-23 to 6'77 centimetres). Passing from the caecum, the canal 

 diminishes in caliber, gradually and very slightly, to where the sigmoid flex- 

 ure 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 caecum, in the 



