THE ABDOMEN 699 



of the jejunum and ileum. Internally coils of the jejunimi and 

 ileum form a superficial relation, whilst more deeply there are 

 the lower part of the left kidney and the left psoas magnus muscle 

 covered by its fascia. The descending colon in most cases is 

 covered by peritoneum in front and at the sides, but not behind. 

 Sometimes, however, it is completely invested by the serous 

 membrane, which then forms behind it a mesenterj', called the 

 descending meso-colon. 



The ascending, transverse, and descending parts of the colon form 

 an arch, within the concavity of which the coils of the jejunum and 

 ileum are disposed. 



Iliac Colon.— This commences at the lower extremity of the 

 descending colon on a level with the back part of the iliac crest, 

 and terminates at the inner border of the left psoas magnus, anterior 

 to' the left sacro-iliac articulation. At this point it enters the pelvic 

 cavity and becomes the pelvic colon. It is situated in the left 

 iliac fossa, where it lies upon the ilio-psoas muscle with the inter- 

 vention of the fascia iliaca, its direction being downwards and 

 inwards. Anteriorly it is covered, when empty, by coils of the 

 ileum, but when distended it lies in contact with the anterior 

 abdominal wall. The iliac colon in most cases is covered by 

 peritoneum in front and at the sides, but not behind. Sometimes, 

 however, it is completely invested by the serous membrane, which 

 then forms behind it a mesentery, called the iliac meso-colon. 



For the pelvic colon and rectum, see p. 859. 



The large intestine, with the exception of the vermiform appendix 

 and rectum, is characterized by weU-marked sacculations, which 

 present a striking contrast to the smooth cylindrical contour of 

 the wall of the small intestine. These sacculations are due to the 

 longitudinal muscular fibres being gathered into three longitudinal 

 bands, called teenies coli (ligaments of the colon), which are shorter 

 than the portion of bowel to which they are applied. The saccula- 

 tions are separated from each other by constrictions filled with fat. 

 Another characteristic of the greater part of the large intestine 

 is the presence, at frequent intervals, of small projections of the 

 peritoneal coat containing fat, called appendices epipioicce. These 

 characteristics will be found described in connection with the 

 structure of the large intestine on p. 795 . 



For the structure and development of the intestinal canal, see 

 Index. 



Position, Connections, and Component Parts of the Spleen.— The 

 spleen (lien) is a ductless gland which lies deeply in the left 

 hypochondrium opposite the ninth, tenth, and eleventh ribs, and 

 extending from about the level of the ninth thoracic spine to that 

 of the eleventh. The organ can only be seen when the stomach 

 is drawn out from the left hypochondrium. It is soft, spongy, 

 easily torn, and exceedingly vascular, and it has a dark red colour. 

 It is so liable to become enlarged that it is subject to much variety 

 as regards dimensions and shape. The following statement, therefore. 



