430 DISSECTION OF THE ABDOMEN. 



takes its unusual course in front of and on the inner side of the neck of 

 the hernia, and will be before the knife in the division of the stricture. 

 As this condition of the vessel cannot be recognized beforehand, the sur- 

 geon will best avoid the danger of wounding the artery by a cautious and 

 sparing use of the knife. 



SECTION III. 



CAVITY OF THE ABDOMEN. 



THE abdominal cavity is the space included between the spinal column 

 behind, and the visceral arches of the vertebrae with their intervening 

 muscles in front. It is lined by a serous membrane (peritoneum), and 

 contains the digestive, urinary, and generative organs, with vessels and 

 nerves. 



Dissection. To prepare the cavity for examination, the remainder of 

 the abdominal wall above the umbilicus is to be cut, along the left side of 

 the linea alba, as far as the xiphoid cartilage. The resulting flaps may be 

 thrown to the sides. 



Size and form. This space is the largest in the body. It is ovoidal in 

 form, with the ends upwards and downwards, so that it measures more 

 in the vertical than the transverse direction ; and it is much wider supe- 

 riorly than inferiorly. 



Boundaries. Above it is limited by the diaphragm ; below by the 

 recto-vesical fascia and the levatores ani, and the structures closing the 

 outlet of the pelvis: both these boundaries are concave towards the cavity, 

 and are in part fleshy, so that the space will be diminished by their con- 

 traction and flattening. 



In front and on the sides the parietes are partly osseous and partly 

 muscular : thus towards the upper and lower limits is the bony frame- 

 work of the skeleton, viz., the ribs in one direction and the pelvis in the 

 other ; but in the centre are stretched the muscles of the abdominal wall. 



Behind is placed the spinal column with the muscles contiguous to it, 

 viz., the psoas and the quadratus lurnborum. 



Alterations in size. The dimensions of the cavity are influenced by 

 the varying conditions of the boundaries. Its depth is diminished by the 

 contraction and descent of the diaphragm, and the contraction and ascent 

 of the levatores ani ; and the cavity is restored to its former dimensions 

 by the relaxation of those muscles. 



The width is lessened by the contraction of the abdominal muscles ; but 

 it is increased, during their relaxation, by the action of the diaphragm 

 forcing outwards the viscera. The greatest diminution of the space is 

 effected by the simultaneous contraction of all the muscular boundaries, 

 as in the expulsion of the excreta. 



Division of the space. A division has been made of the space into the 

 abdomen proper and the cavity of the pelvis. 



The abdominal portion reaches from the diaphragm to the brim of the 

 pelvis, and lodges the alimentary tube and its appendages, together with 

 the kidneys. 



