ABDOMINAL CAVITY 547 



superiorly, it contracts and becomes the thoracic duct. 

 About its middle it is joined anteriorly by the- intestinal 

 trunk. Entering it near its upper end are two lymph 

 trunks which come from the lower intercostal glands ; 

 they reach it by passing downwards through the aortic 

 opening. The vena azygos lies along its right side, but the 

 cisterna chyli is easily distinguished from this by the whiteness 

 of its walls. The thoracic duct enters the thorax by passing 

 through the aortic opening of the diaphragm. 



The Azygos Vein. The azygos vein (O.T. vena azygos major] 

 usually takes origin in the right ascending lumbar vein. It 

 will be found in the interval between the right crus of the 

 diaphragm and the aorta, upon the right side of the cisterna 

 chyli, and it will be noticed to enter the thorax by passing 

 through the aortic opening of the diaphragm. 



The Hemiazygos Vein (O.T. Vena Azygos Minor Inferior) 

 is more difficult to discover. It originates on the left side of 

 the spine, in the left ascending lumbar vein, and enters the 

 thorax by piercing the left crus of the diaphragm. 



FASCIA AND MUSCLES ON THE POSTERIOR WALL 

 OF THE ABDOMEN. 



The muscles on the posterior wall of the abdomen are 

 three in number, viz. (i) the psoas magnus, an elongated 

 fleshy mass extending downwards on the side of the spine ; 

 (2) the quadratus lumborum, a quadrate muscle external to 

 the psoas, and stretching between the crest of the ilium and 

 the last rib ; (3) the iliacus, situated in the iliac fossa. The 

 fascia which covers these muscles must be studied first. 



Quadratus Lumborum Fascia. Follow this medially and 

 it will be found to be attached to the medial ends of the 

 anterior surfaces of the transverse processes of the lumbar 

 vertebrae. Trace it laterally and it will be noticed to join the 

 posterior aponeurosis of the transversus abdominis muscle. 

 From these connections the dissector will understand that this 

 fascia is simply the anterior lamella of the lumbar fascia. 

 Above, it is fixed to the last rib, and is thickened so as to form 

 the arcus lumbo-costalis lateralis, whilst inferiorly it is attached 

 to the ilio-lumbar ligament. The quadratus lumborum muscle, 

 therefore, is enclosed in a sheath formed anteriorly by the 



