The lateral walls of the abdomen are like wise completely lined by peritoneum, which extends backwards as far as the junction of these walls with the posterior, where it is re flected from them so as to involve the ascending colon on the right side and the descending on the left, and here it forms on each side the folds respectively termed right and left meso colon. From the right lateral wall the peri toneum is continued upwards upon the dia phragm, and contributes to form the right lateral ligament of the liver; on the left side it is continued in a similar manner on the diaphragm, and in passing from the spleen to that muscle forms the fold called splenico phrenic.
The concave surface of the diaphragm is in greatest part lined by peritoneum : the an terior half of the muscle is uninterruptedly covered by peritoneum, which adheres very closely to the central tendon, but is much more easily separated from the muscular portion. On the right side and in the middle, in front of the cesophageal opening, the peritoneum is re flected from the diaphragm to the liver, forming the right lateral, coronary, and left lateral liga ments of that organ. The posterior half of this surface is likewise covered by peritoneum, that membrane being deficient for a little way behind the opening for the vena cava and behind and on each side of the cesophageal and aortic openings : the crura of the diaphragm are covered chiefly on the outer side.
The peritoneum comes into immediate con tact with the posterior abdominal wall only in a very small portion of its extent : in tracing it on the right side we find it covering the right colon, then passing inwards over the kidney and suprarenal capsule, the duodenum and vena cava, to the crus of the diaphragm above, and in the middle and below, where it also covers the vena cava, and the renal vessels, to form the right or superior lamina of the mesentery. On the left side it covers in a similar manner the left colon, the left kidney and capsule, and that portion of small intestine which projects just to the left of the superior mesenteric artery, which may be regarded as the commencement of the jejupum ; below this it manifests its continuity with the layer of the opposite side by forming the left or inferior lamina of the mesentery. This lamina commences at the left side of the body of the second lumbar vertebra ; as it descends, it gradually crosses more in front of the aorta, so as to terminate at the right sacro-iliac symphysis ; the right lamina is situated quite on the right side of the spine.
In the iliac fossa the peritoneum is in con nexion with the fascia iliaca, except where it is separated by the ccecum on the right side (on which side it sometimes forms a fold termed mesoccecum,) and by the sigmoid flexure on the left. Internal to these portions of intestine on each side, the peritoneum covers the ex ternal iliac artery and vein, from which it is separated by a very loose and sometimes adi pose cellular tissue, and by a process of the iliac fascia, to which allusion has already been made.
From the preceding description of the con nection of the peritoneum with the parietes of the abdomen, it will appear how few are the situations at which the surgeon could cut through any portion of these walls without risk of wounding the serous membrane. Im mediately above the pubis this may be done in consequence of the abundance of cellular membrane there which separates the serous membrane from the wall ; but in the con tracted state of the bladder the operator must proceed with the greatest caution : in the dis tended state of that viscus, however, the wall of the abdomen is deprived of its lining to an extent proportionate to the height to which the bladder ascends behind the recti muscles; and accordingly it is under such circumstances that the paraccmtesis vesica supra pubem, and the high operation for the stone may be per formed with impunity to the serous membrane. At the posterior wall an instrument may be passed into any part of the posterior surface of the kidney without injury to the peritoneum; the pelvis of the kidney, or any part of the abdominal course of the ureter, may be opened too, or the vena cava; and by cutting into the bodies of the vertebra, and the muscular por tion of the posterior wall in the dead body, a view of all the parts which lie upon that wall may be obtained without at all injuring the peritoneum.* Further details respecting the anatomy of the peritoneum will be found in the article under that head.
Vessels and nerves of the abdominal walls.— a. The arteries.—The most important arterial ramifications are found in the anterior wall. In the superficial fascia we find the superficial epigastric artery or tegumentary artery, which exists as a trunk in the iliac regions. This artery, arising from the femoral, pierces the fascia lata, and passes over Poupart's ligament upwards and inwards, crossing the anterior wall of the inguinal canal between the two rings ; it is distributed in the integuments and fascia of the iliac and umbilical regions, and anas tomoses with its fellow of the opposite side, and by deep branches which pierce the aponeuroses, with the deep epigastric artery. In the epigas trium and hypochondria the superficial fascia and integument are supplied by cutaneous branches from the internal mammary and the inferior intercostals. The deep-seated parts of this region are likewise supplied from the last named arteries ; the largest and most constant of which is the abdominal branch of the internal mammary, which in the sheath of the rectus supplies that muscle, and establishes an im portant communication with the epigastric this anastomosis is said to have been known to Galen, who by it proposed to account for the sympathy which exists between the uterus and the breasts.* Another branch of the mammary supplies the muscles external to the rectus ; it runs between the obliquus internus and trans versalis, and is lost in anastomosing with the inferior intercostal, the lumbar, and the circum flexa ilii arteries.