THE ABDOMEN. 895 



THE ABDOMEN. 



The Abdomen is the largest cavity in the body. It is of an oval form, the 

 extremities of the oval being directed upward and downward : the upper one 

 being formed by the under surface of the Diaphragm, the lower by the upper 

 concave surface of the Levatores ani. In order to facilitate description, it is 

 artificially divided into two parts : an upper and larger part, the abdomen proper ; 

 and a lower and smaller part, the pelvis. These two cavities are not separated 

 from each other, but the limit between them is marked by the brim of the true 

 pelvis. The space is wider above than below, and measures more in the vertical 

 than in the transverse diameter. 



The abdomen proper differs from the other great cavities of the body in being 

 bounded for the most part by muscles and fasciae, so that it can vary in capacity 

 and shape according to the condition of the viscera which it contains ; but, in 

 addition to this, the abdomen varies in form and extent with age and sex. In 

 the adult male, with moderate distention of the viscera, it is oval or barrel-shaped, 

 but at the same time flattened from before backward. In the adult female, with a 

 fully developed pelvis, it is conical with the apex above, and in young children it 

 is conical with the apex below. 



Boundaries. The boundary between the thorax and abdomen is the Diaphragm. 

 This muscle forms a dome over the abdomen, and the cavity extends high into the 

 bony thorax, reaching to the level of the junction of the fourth costal cartilage 

 with the sternum. The lower end of the abdomen is limited by the structures 

 Avhich clothe the inner surface of the bony pelvis, principally the Levatores arii 

 and Coccygei muscles on either side. These muscles are sometimes termed the 

 Diaphragm of the pelvis. The abdomen proper is bounded in front and at the 

 sides by the lower ribs, the abdominal muscles, and the venter ilii ; behind, by the 

 vertebral column and the Psoas and Quadratus lumborum muscles; above, by the 

 Diaphragm ; below, by the brim of the pelvis. The muscles forming the boundaries 

 of the cavity are lined upon their inner surface by a layer of fascia, differently 

 named, according to the part which it covers. 



The abdomen contains the greater part of the alimentary canal ; some of the 

 accessory organs to digestion, viz., the liver and pancreas ; the spleen, the kidneys, 

 and suprarenal capsules. Most of these structures, as well as the wall of the 

 cavity in which they are contained, are covered by an extensive and complicated 

 serous membrane, the peritoneum. 



The apertures found in the walls of the abdomen, for the transmission of 

 structures to or from it, are, the umbilicus, for the transmission (in the foetus) of 

 the umbilical vessels ; the caval opening in the Diaphragm, for the transmission 

 of the inferior vena cava ; the aortic opening, for the passage of the aorta, vena 

 azygos major, and thoracic duct; and the oesophagcal opening, for the oesophagus 

 and pneumogastric nerves. Below, there are two apertures on each side : one for 

 the passage of the femoral vessels, and the other for the transmission of the 

 spermatic cord in the male, and the round ligament in the female. 



Regions. For convenience of description of the viscera, as well as of reference 

 to the morbid conditions of the contained parts, the abdomen is artificially divided 

 into nine regions. Thus, if two circular lines are drawn round the body, the one 

 through the extremities of the ninth ribs where they join their costal cartilages, and 

 the other through the highest point of the crests of the ilia, the abdominal cavity 

 is divided into three zones an upper, a middle, and a lower. If two parallel lines 

 are drawn perpendicularly upward from the centre of Poupart's ligament, each of 

 these zones is subdivided into three parts a middle and two lateral. 



1 Anatomists are far from agreed as to the best method of subdividing the abdominal cavity. 

 Cunningham suggests that the lower line should encircle the body on a level with the highest point 

 of the iliac crest, as seen from the front a point corresponding with a prominent tubercle "on the 

 outer lip of the iliac crest about two inches behind the anterior superior spine. Addison, 1 in a 

 careful analysis of the abdominal viscera in forty subjects, adopts the following lines : (1) a median, 



1 Journal of Anatomy and Physiology, vols. xxxiv. and xxxv. 



