THE ABDOMINAL CAVIIY. 451 



termed the "viscera." The anterior, the smallest, is the pectoral or thoracic 

 cavity ; the posterior is named the abdonmi, or abominal cavity. 



Form of the Abdominal Cavity. — The abdomen is a vast oval-shaped reservoir, 

 elongated from before to behind, having for its upper wall the muscles of the 

 sublumbar region, enclosed below and laterally by the muscles of the inferior 

 abdominal region, bounded in front by the diaphragm, and prolonged behind 

 between the bones and membranous ligaments of the pelvis. 



The parts forming the walls of this cavity having been already described, we 

 will confine ourselves to an examination of its interior, in order to determine the 

 various regions into which it is possible to divide it — a matter of some impor- 

 tance, as it singularly facilitates the topographical study of the contained viscera ; 

 for to say that an organ is situated in the abdomen, is a very vague reference to 

 its precise situation, in consequence of the great extent of this cavity. It is 

 necessary, therefore, to divide the abdomen into a certain number of peripheral 

 regions which will correspond to the diiferent parts of its wall, with a view to 

 define the situation of the organs lodged therein, yet without complicating 

 anatomical description. Six principal regions are recognized in the abdominal 

 cavity. 



A. The superior, or sublumbar regior),, corresponds to the superior wall of the 

 abdomen ; that is, to the psoas muscles and the bodies of the lumbar vertebrae. 

 It extends from the opening between the two pillars of the diaphragm to the 

 entrance to the pelvis. 



B. The inferior region, limited, laterally, by the hypochondriacs and the 

 flanks, commences, in front, at the xiphoid cartilage, and is prolonged to the 

 pubis ; it comprises all that portion of the abdomen which corresponds to 

 the linea alba and the two recti muscles. Its great extent necessitates its sub- 

 division into five secondary regions : The supra-sternal region, named the epigastric 

 in Man, placed above the xiphoid cartilage of the sternum ; the umbilical region, 

 situated behind the preceding, and so named in consequence of its including that 

 part of the wall which is pierced by the umbilicus ; the prejmbic region — the 

 hypogastric or pubic of Man — occupies the space in front of the anterior border 

 of the pubis ; the two inguinal regions, diverticuli of the abdominal cavity, located 

 in the inguinal tracts, where they form the special reservoirs to be hereafter 

 described as the vaginal sheaths (or inguinal canals). 



C. The lateral regions {right and left lumbar of Man) are limited : in front, 

 by the costal attachments of the diaphragm ; behind, by the entrance to the 

 pelvic cavity ; above, by the superior border of the small oblique muscle ; below, 

 by the interval comprised between the inferior border of that muscle and the 

 external border of the great rectus muscle. The designation of hypochondriac 

 is given to the sub-region which corresponds to the cartilaginous circle of the 

 false ribs. The fianlc is that section covered by the muscular portion of the 

 small oblique muscle. 



D. The anterior, or diaphragmatic region, comprises the cavity formed by the 

 posterior face of the diaphragm. Like that muscle, it is divided into two regions, 

 a central and peripheral. 



E. The posterior, or ^;e/i?ic region, is a special diverticulum of the abdomen 

 described as the pelvic cavity. It is bounded, above, by the sacrum ; below, by 

 the superior face of the pubes, the ischia, and the internal obturator muscle ; on 

 the sides, by the constricted portions of the ossa innominata and the sacro-sciatic 

 ligaments. The entrance to this diverticulum is situated above the pubes and 



