THE ABDOMEX. 959 



There may exist a congenital deformity in the anterior wall, a partial lack of 

 development and an ununited symphysis pubis ; with this the anterior wall of the 

 bladder is lacking and its posterior wall, with ureters, exposed. This condition 

 is called exstrophy of the bladder. 



The jioxfr //'>/ "'nil of the abdomen proper has no special line of demarcation 

 from the antero-lateral Avail ; its vertical length is of much less extent than the 

 latter (Fig. 570). 



It is the part into which the skeleton enters, composed of the five lumbar 

 vertebrae connected by ligaments and disks. Laterally are the Psoas and Quad- 

 ratus lumborum muscles, and behind these the Sacro-spinalis mass (Erector spinse 

 muscle). 



Through the lumbar region on either side of the vertebral column the folio w- 



c i 



ing structures are met in order : 



1. Skin. 



2. Subcutaneous fascia and cellular tissue. 



3. Lumbar aponeurosis, posterior layer. 



4. Erector spinse muscle. 



5. Transverse process and lumbar aponeurosis, middle layer. 



6. Quadratus lumborum muscle. 



7. Lumbar aponeurosis, anterior layer. 



8. Psoas muscle. 



9. Visceral layer of kidney, cellular tissue, and colon. 



10. Subperitoneal tissue and peritoneum. 



This region presents the special districts, lumbar and iliac, already described. 

 The arteries, veins, nerves, and lymphatics are all called lumbar. 



The roof and floor of the abdomen are elsewhere described. 



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, and thoracic duct ; and the oesophageal opening, for the ossophagus and 

 pneumogastric nerves. Beloiv, 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. 



THE ABDOMINAL CAVITY AND CONTEXTS. 



It must be carefully noted that there is a difference between the abdominal 

 cavity proper and the peritoneal cavity. The peritoneum does not closely cover 

 everywhere the abdominal walls, but is pushed in and out, leaving spaces and 

 diverticula so that some organs will be extraperitoneal, others intraperitoneal, 

 yet all will be inside the abdominal cavity. 



Before studying the peritoneum it will be best to become more familiar with 

 the names and location of the important viscera. This can be shown in a topo- 

 graphical way by dividing off the surface of the abdomen into districts and con- 

 sidering the chief organs lying in each. 



Regions. 



Many authors have devised many means for this subdivision, all of which 

 consist in allowing two horizontal planes to cross two perpendicular ones ; the 

 edges of these planes are indicated by lines on the abdomen. An old way was 

 to let the edge of one horizontal plane intersect the anterior extremities of the 

 ninth ribs, and to let the lower plane pass through the highest points of the 

 crests of the ilia. The perpendicular planes passed each one through the centre 

 of Poupart's ligament. 



The advantage of the following method (Joessel) is that all its planes pass 

 through bony points and its two perpendicular planes through the brim of the 



