THE LARGE INTESTINE 1177 



the lymphatics from the mucous membrane, and empty themselves in the same manner as 

 these into the origins of the lacteal vessels at the attached border of the gut. 



The nerves of the small intestines are derived from the plexuses of sympathetic nerves around 

 the superior mesenteric artery. From this source they run to the myenteric plexus (Auerbach's 

 plexus) (Fig. 1071) of nerves and ganglia situated between the circular and longitudinal mus- 

 cular fibers from which the nervous branches are distributed to the muscular coats of the 

 intestine. From this a secondary plexus, the plexus of the submucosa (Meissner's plexus) 

 (Fig. 1072) is derived, and is formed by branches which have perforated the circular muscular 

 fibers. This plexus lies in the submucous coat of the intestine; it also contains ganglia from 

 which nerve fibers pass to the muscularis mucosae and to the mucous membrane. The nerve 

 bundles of the submucous plexus are finer than those of the myenteric plexus. 



The Large Intestine (Intestinum Crassum). 



The large intestine extends from the end of the ileum to the anus. It is about 

 1.5 meters long, being one-fifth of the whole extent of the intestinal canal. Its 

 caliber is largest at its commencement at the cecum, and gradually diminishes 

 as far as the rectum, where there is a dilatation of considerable size just above 

 the anal canal. It differs from the small intestine in its greater caliber, its more 

 fixed position, its sacculated form, and in possessing certain appendages to its 

 external coat, the appendices epiploicae. Further, its longitudinal muscular fibers 

 do not form a continuous layer around the gut, but are arranged in three longitudinal 

 bands or tsenise. The large intestine, in its course, describes an arch which sur- 

 rounds the convolutions of the small intestine. It commences in the right iliac 

 region, in a dilated part, the cecum. It ascends through the right lumbar and hypo- 

 chondriac regions to the under surface of the liver; it here takes a bend, the right 

 colic flexure, to the left and passes transversely across the abdomen on the confines 

 of the epigastric and umbilical regions, to the left hypochondriac region; it then 

 bends again, the left colic flexure, and descends through the left lumbar and iliac 

 regions to the pelvis, where it forms a bend called the sigmoid flexure; from this it 

 is continued along the posterior wall of the pelvis to the anus. The large intestine 

 is divided into the cecum, colon, rectum, and anal canal. 



The Cecum (intestinum caecum} (Fig. 1073), the commencement of the large 

 intestine, is the large blind pouch situated below the colic valve. Its blind end 

 is directed downward, and its open end upward, communicating directly with the 

 colon, of which this blind pouch appears to be the beginning or head, and hence the 

 old name of caput caecum coli was applied to it. Its size is variously estimated by 

 different authors, but on an average it may be said to be 6.25 cm. in length and 7.5 in 

 breadth. It is situated in the right iliac fossa, above the lateral half of the inguinal 

 ligament : it rests on the Iliacus and Psoas major, and usually lies in contact with the 

 anterior abdominal wall, but the greater omentum and, if the cecum be empty, 

 some coils of small intestine may lie in front of it. As a rule, it is entirely enveloped 

 by peritoneum, but in a certain number of cases (5 per cent., Berry) the peritoneal 

 covering is not complete, so that the upper part of the posterior surface is uncovered 

 and connected to the iliac fascia by connective tissue. The cecum lies quite free 

 in the abdominal cavity and enjoys a considerable amount of movement, so that 

 it may become herniated down the right inguinal canal, and has occasionally 

 been found in an inguinal hernia on the left side. The cecum varies in shape, but, 

 according to Treves, in man it may be classified under one of four types. In early 

 fetal life it is short, conical, and broad at the base, with its apex turned upward 

 and medialward toward the ileocolic junction. It then resembles the cecum of some 

 monkeys, e. g., mangabey monkey. As the fetus grows the cecum increases in 

 length more than in breadth, so that it forms a longer tube than in the primitive 

 form and without the broad base, but with the same inclination of the apex toward 

 the ileocolic junction. This form is seen in other monkeys, e. g., the spider monkey. 

 As development goes on, the lower part of the tube ceases to grow and the upper 



n.o ucvcii 



