THE ABDOMEN 761 



right and left pneumogastric nen'es, and the oesophageal branches 

 of the gastric artery. 



In addition to the foregoing foramina, the diaphragm presents certain small 

 fissures, as follows : each crus is pierced by the great and small splanchnic 

 nerves, and sometimes by the least. The left crus is also pierced by the lower 

 left azygos vein. The musculo-phrenic artery pierces the costal portion, and 

 the branches of the phrenic nerve are also transmitted through the muscle. 



The arcuate ligaments are five in number, as follows : external, 

 right and left ; internal, right and left ; and middle. The external 

 arcuate ligament is a thickening of the upper part of the anterior 

 wall of the sheath of the quadratus lumborum, and extends from 

 the last rib to the tip of the transverse process of the first lumbar 

 vertebra. The subcostal artery and nerve pass downwards and 

 outwards behind it. The internal arcuate ligament is a thickening 

 of the upper part of the sheath of the psoas magnus, and extends 

 from the tip of the transverse process of the first lumbar vertebra 

 to the side of its body. The gangliated cord of the sympathetic 

 passes into the abdomen behind it, and sometimes the least 

 splanchnic nerve. The middle arcuate ligament is a fibrous band 

 which connects the innermost tendinous fibres of the crura on 

 a level with the lower border of the body of the twelfth thoracic 

 vertebra, and it arches over the aorta. 



Relations of the Diaphragm — Superior. — The right and left pleurae with 

 the lungs, and the pericardium with the heart. Inferior. — The peritoneum, 

 except opposite the uncovered area of the posterior surface of the liver ; the 

 liver with its suspensory, coronary', and right and left lateral or triangular 

 ligaments ; the stomach ; spleen ; pancreas ; kidneys ; and suprarenal capsules. 



Development. — The diaphragm is develop)ed in two parts — ventral and 

 dorsal. The ventral part, which is the first to appear, is developed from the 

 upper layer of the septum transversum. It shuts off the pericardial cavity 

 from the peritoneal cavity, leaving t^vo passages, one on each side of the 

 primitive ahmentary tube, which are called the thoracic prolongations of the 

 peritoneal cavity, and which are destined to form the pleural cavities. 



The dorsal part of the diaphragm is developed from the two plearo-peri- 

 toneal membranes, formed by the pleuro-peritoneal folds, which grow from 

 the dorsal and lateral body-walls, and which close the primitive pleuro-peri- 

 toneal openings on either side. The fusion betsveen these pleuro-peritoneal 

 membranes and the ventral part of the diaphragm may be incomplete on one 

 or other side, in which cases a communication is left between the thoracic 

 and abdominal cavities, through which a diaphragmatic hernia may occur. 



Gangliated Cord of the Sympathetic. — ^This cord enters the abdo- 

 men behind the inner portion of the internal arcuate ligament. 

 It then descends along the inner border of the psoas magnus, where 

 it lies in front of the bodies of the lumbar vertebrae, and, having 

 passed behind the common iliac artery, it enters the pelvis. The 

 right lumbar cord is under cover of the inferior vena cava, whilst 

 the left lies a little to the left of the aorta, and the lumbar vessels 

 of each side pass beneath the corresponding cord. Each cord 

 usually contains four ganglia. 



Branches. — These are arranged in two sets, namely, rami com- 

 municantes, and branches of distribution. The rami communic antes, 

 which are long, are of two kinds, white and grey, the latter being 



