538 DIGESTION. 



exert considerable influence on the digestive function, requires a brief 

 description. It is the division of the body, which is betwixt the thorax 

 and pelvis; is bounded, above, by the arch of the diaphragm; behind, 

 by the vertebral column ; laterally, and anteriorly, by the abdominal 

 muscles; and, below, by the ossa ilii, os pubis, and the cavity of the 

 pelvis. 



To connect the knowledge of the internal parts of the abdomen with 

 the external, it is customary to mark certain arbitrary divisions on the sur- 

 face, called regions. (Fig. 245.) The epigastric region is at the upper 

 portion of the abdomen, under the point of the sternum, and in the angle 

 formed by the cartilages of the ribs. The hypochondriac regions are 

 covered by the cartilages of the ribs. These three regions the epigas- 

 tric, and right and left hypochondre constitute the upper division of the 

 abdomen, in which are seated the stomach, liver, spleen, pancreas, duo- 

 denum, and part of the arch of the colon. The space surrounding the 

 umbilicus, between the epigastric region and a line drawn from the crest 

 of one os ilii to the other, is the umbilical region. Here the small intes- 

 tines are chiefly situate. This region is bounded by lines, raised per- 

 pendicularly to the spine of the ilium; and the lateral portions on the 

 outside of these lines, form the iliac regions, behind which, again, are 

 the lumbar regions or loins. In these, the colon and kidneys are chiefly 

 situate. The hypogastric is, likewise, divided into three regions, the 

 pubic in the middle, in which is the bladder; and an inguinal on each 

 side. 



The muscles that constitute the abdominal parietes, are, first of all, 

 above, the diaphragm, which is the boundary between the thorax and 

 abdomen, convex towards the chest, and considerably concave towards 

 the abdominal cavity. Below, if we add the pelvic cavity, which, as 

 it contains the rectum, and muscles concerned in the evacuation of the 

 faeces, it may be proper to do, the cavity is bounded by the perineum, 

 formed chiefly of the levatores ani and coccygei muscles. Behind, la- 

 terally, and anteriorly, from the lumbar vertebrae round to the umbilicus, 

 the parietes consist of planes of muscles, and aponeuroses in super- 

 position, united at the median line, by a solid, aponeurotic band, extend- 

 ing from the cartilago-ensiformis of the sternum to the pubes, called 

 tinea alba. The abdominal muscles, properly so called, are, reckoning 

 the planes from within to without, the greater oblique muscle, lesser 

 oblique, and transversalis, which are situate chiefly at the sides of the 

 abdomen; and the rectus and pyramidalis, which occupy the anterior 

 part. The greater oblique, obliquus externus, costo-abdominalis ; lesser 

 oblique, obliquus internus, ilio-abdominalis, and transversalis, transver- 

 sus abdominis, lumbo-abdominalis, support and compress the abdominal 

 viscera ; assist in the evacuation of the faeces and urine, and in the 

 expulsion of the foetus; besides other uses, connected with respiration 

 and the attitudes. The rectus, pubio-sternalis or sterno-pubialis ; and 

 the pyramidalis or pubio-subumbilicalis, are more limited in their action, 

 and compress the forepart of the abdomen; besides having other 

 functions. 



Lastly, a serous membrane the peritoneum lines the abdomen, and 

 gives a coat to most of the viscera. The mode, in which its various 



