ALIMENTARY CANAL AND ITS APPENDAGES 411 



presents the same coats as the small. The external stratum of the 

 muscular coat is not, however, developed uniformly around it, 

 except on the rectum, but occurs in three bands separated by in- 

 tervals in which it is wanting. These bands being shorter than the 

 rest of the tube cause it to be puckered, or sacculated, between 

 them. The mucous coat possesses no villi or valvuhc conniventcs, 

 but is usually thrown into cffaceable folds, like those of the 

 stomach but smaller. It contains numerous closely set glands 

 much like the crypts of Lieberkiihn of the small intestine. 



The Ileocolic Valve. Where the small intestine joins the large 

 there is a valve, formed by two flaps of the mucous membrane slop- 

 ing down into the colon, and so disposed as to allow matters to 

 pass readily from the ilcum into the large intestine but not the 

 other way. 



The Nerves of the Intestines. The intestines arc innervated 

 through sympathetic nerves. These come to them by way of two 

 main channels; from the sympathetic system proper the splanchnic 

 nerves pass to the intestines; their other chief channel of inncrva- 

 tion is by way of the vagi. Both these sets of nerves ramify in the 

 solar plexus; from here nerve strands pass to the intestine, as well 

 as to the stomach, along the mesentery. There are also fibers 

 passing to the intestines from the mescnteric plexus lying in the 

 lower part of the abdomen, these fibers reach that plexus from the 

 posterior thoracic and anterior lumbar sympathetic ganglia. 



The intestines are provided, in addition, with an intrinsic inncr- 

 vation consisting of two nervous networks or plexuses lying, one 

 between the mucosa and the muscular coat, the plexus of Meissner, 

 and the other between the circular and longitudinal muscle layers, 

 the plexus of Auerbach. 



The Liver. Besides the secretions formed by the glands em- 

 bedded in its walls, the small intestine receives those of two large 

 glands, the liver and the pancreas, which lie in the abdominal 

 cavity. The ducts of both open by a common aperture into the 

 duodenum about 10 centimeters (4 inches) from the pylorus. 



The liver is the largest gland in the Body, weighing from 1,400 to 

 1,700 grams (50 to (>1 ounces). It is situated in the upper part of 

 the abdominal cavity (/.-. /'. Fig. 1), rather more on the right than 

 on the left side and immediately below the diaphragm, into the 

 concavity of which its upper surface fits, and reaches across the 



