922 THE ORGANS OF DIGESTION. 



voluted, and forms the sigmoid flexure ; finally it enters the pelvis, and descends 

 along its posterior wall to the anus. The large intestine is divided into the 

 caecum, colon, and rectum. 



The Caecum (csecus, blind) is the large blind pouch, or cul-de-sac, situated below 

 the ileo-caecal valve, in which the large intestine commences (Fig. 506). 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 caput ccecum coli was applied to it. Its size is variously estimated 

 by different authors, but on an average it may be said to be two and a half inches 

 in length and three in breadth. It is situated in the right iliac fossa, above the 

 outer half of Poupart's ligament : it rests on the Ilio-psoas muscle and lies imme- 

 diately behind the abdominal wall. As a rule, it is entirely enveloped on all sides 

 by peritoneum, but in a certain number of cases (6 per cent., Berry) the peritoneal 

 covering is not complete, so that a small portion of the upper end of the posterior 

 surface is uncovered and connected to the iliac fascia by connective tissue. The 

 caecum lies quite free in the abdominal cavity and enjoys a considerable amount of 

 movement, so that it often becomes herniated down the right inguinal canal, and 

 has occasionally been found in an inguinal hernia on the left side. The caecum 

 varies in shape, but, according to Treves, in man it may be classified under one of 

 four types. In early foetal life it is short, conical, and broad at the base, with its 

 apex turned upward and inward toward the ileo-caecal junction. It then resembles 

 the caecum of some of the monkey tribe, e. $., Mangabey monkey. As the foetus 

 grows the caecum 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 inward of the apex toward the ileo-csecal junction. This form is seen 

 in others of the monkey tribe, e. g., the spider monkey. As development goes on, 

 the lower part of tube ceases to grow and the upper part becomes greatly increased, 

 so that at birth there is a narrow tube, the vermiform appendix, hanging from a 

 conical projection, the caecum. This is the infantile form, and as it may persist 

 throughout life, in about 2 per cent, of cases, it is regarded by Treves as the first 

 of his four types of human caeca. The caecum is conical and the appendix rises 

 from its apex. The three longitudinal bands start from the appendix and are 

 equidistant from each other. In the second type, the conical caecum has become 

 quadrate by the growing out of a saccule on either side of the anterior longitudinal 

 band. These saccules are of equal size, and the appendix arises from between 

 them, instead of from the apex of a cone. This type is found in about 8 per cent, 

 of cases. The third type is the normal type of man. Here the two saccules, 

 which in the second type were uniform, have grown at unequal rates : the right 

 with greater rapidity than the left. In consequence of this an apparently new 

 apex has been formed by the growing downward of the right saccule, and the 

 original apex, with the appendix attached, is pushed over to the left toward the 

 ileo-caecal junction. The three longitudinal bands still start from the base of the 

 appendix, but they are now no longer equidistant from each other, because the right 

 saccule has grown between the anterior and postero-external bands, pushing them 

 over to the left. This type occurs in about 90 per cent, of cases. The fourth 

 type is merely an exaggerated condition of the third ; the right saccule is still 

 larger, and at the same time the left saccule has been atrophied, so that the original 

 apex of the caecum, with the appendix, is close to the ileo-caecal junction, and the 

 anterior band courses inward to the same situation. This type is present in about 

 4 per c^nt. of cases. 



The vermiform appendix is a long, narrow, worm-shaped tube, which starts 

 from what was originally the apex of the caecum, and may pass in several direc- 

 tions : upward behind the caecum ; to the left behind the ileum and mesentery ; 

 or downward and inward into the true pelvis. It varies from one to nine inches in 

 length, its average being about three inches. It is retained in position by a fold 

 of peritoneum derived from the left leaf of the mesentery, which forms a mesentery 

 for it. This is triangular in shape, but does not extend the whole length of the 



