PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE 225 



offering an elastic but resisting mass upon which the compressing 

 action of the abdominal muscles may be exerted in straining and in 

 expiration. 



There can be hardly any question that the normal movements 

 of the intestine are due principally to the impression made on the 

 mucous membrane by the alimentary matters, to which may be added, 

 perhaps, the stimulating action of the bile. The vigorous peristaltic 

 movements that occur soon after death have been explained in various 

 ways. It has been shown that these movements are not due to a 

 lowering of the temperature or to exposure of the intestines to the air. 



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 entire 

 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 between the longitudinal and circular layers of the 

 muscular coat. This is known as Auerbach's plexus. From this 

 plexus, fine non-medullated filaments are given off, which form a wider 

 plexus, also with ganglion-cells, situated just beneath the mucous mem- 

 brane. This is called the plexus of Meissner. In experiments on the 

 lower animals it has been shown that stimulation of the pneumogastrics 

 excites peristaltic movements of the intestines ; but in some animals 

 these nerves seem to contain inhibitory as well as motor fibres, although 

 it is probable that the principal inhibitory nerves belong to the sym- 

 pathetic system. Observations on these points, however, are somewhat 

 conflicting. 



It is difficult to estimate the time occupied in intestinal digestion 

 and absorption in man. In the dog the small intestine is nearly empty 

 in six to nine hours after full feeding, but in the carnivora the intestine 

 is relatively short and the indigestible residue of food is small (Halli- 

 burton). In the human subject, the passage of an ordinary meal 

 through the small intestine occupies probably about twelve hours 

 (Kirkes). 



PHYSIOLOGICAL ANATOMY OF THE LARGE INTESTINE 



The length of the large intestine is about five feet (1.5 meter). Its 

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

 distended, two and a half to three and a half inches (6.35 to 8.89 centi- 

 meters). 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 centimeters). Pass- 

 ing from the caecum, the canal diminishes in calibre, gradually and very 



Q 



