6 - ORGANS OF DIGESTION. 



in thin subjects, is almost in contact with the linea alba in 

 front, and may be easily distinguished through the parietes 'of 

 the abdomen, when the intestines are empty. 



The abdominal cavity varies only, inconsiderably, in its ver- 

 tical diameter, owing to the resistance of the diaphragm above, 

 and of the pelvis below; neither does it change behind, owing to 

 the resistance of the spine, the ribs, and the muscles there. But 

 as the introduction of food, the development of gaseous sub- 

 stances during digestion, the evolution of the foetus, and many 

 other conditions, require some provision for its undergoing an 

 easy augmentation of volume; the latter occurs principally for- 

 wards and laterally, by the yielding of the muscles and by the 

 extension of their aponeuroses. 



The diaphragm and the abdominal muscles, for the most part, 

 act alternately; as the former descends in inspiration the latter 

 relax and give way to the contents of the abdomen; but in ex- 

 piration, the abdominal muscles contract, and the diaphragm is 

 pushed upwards by the viscera. In attempts at the expulsion 

 of faeces, and in parturition, these muscles contracting, and the 

 diaphragm being fixed all at the same moment, the cavity of 

 the abdomen is actually much diminished. 



The viscera contained in the cavity of the abdomen are of 

 three kinds. One kind is engaged in digestion and assimilation; 

 another in secretion and excretion of urine; and the third in 

 generation. As these viscera are numerous, and it is of great im- 

 portance to determine with precision their position and relative 

 situation, anatomists are agreed to divide the cavity of the ab- 

 domen into several arbitrary regions. This is the more advan- 

 tageous, as the bony prominences bounding the abdomen are 

 not sufficiently numerous and distinct, to afford those obvious 

 points of relation to the viscera which are furnished in other sec- 

 tions of the body. To obtain these regions, consider a line or 

 plane as extending across the abdomen, about two inches below 

 the umbilicus, from the superior part of the crista of one ilium, 

 as it appears through the skin, to the corresponding place of the 

 other side. Strike on each side a line perpendicular to the pre- 

 ceding, by commencing at the lower end of the anterior inferior 

 spinous process of the ilium, and carrying it up to the dia- 

 phragm. Extend a fourth line across the abdomen parallel with 

 the first, and intersecting the last two where they come upon 



