ABDOMINAL CAVITY 399 



chyli. It enters the thorax by passing through the aortic 

 opening of the diaphragm. 



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

 The hemiazygos vein is more difficult to discover. It originates 

 on the left side of the vertebral column, usually as the con- 

 tinuation of the left ascending lumbar vein, but, occasionally, 

 it springs from the left renal vein. It enters the posterior 

 mediastinum of the thorax after 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 on 

 each side are three in number, viz. (i) the psoas major^ 

 an elongated fleshy mass which lies on the side of the vertebral 

 column; (2) the quadratus lumborum^ a quadrate muscle 

 lateral to the psoas, and extending from the crest of the ilium 

 to the last rib; (3) the iliacus^ situated in the iliac fossa. 

 The fascia which covers the muscles must be studied first. 



Quadratus Lumborum Fascia. When the fascia which 

 covers the anterior surface of the quadratus lumborum muscle 

 is followed medially it will be found to be attached to the 

 medial ends of the anterior surfaces of the transverse processes 

 of the lumbar vertebrae. Traced laterally it will be found 

 to join the posterior aponeurosis of the transversus abdominis 

 muscle. The dissector will understand, from the connections 

 of the fascia, that it is simply the anterior lamella of the 

 lumbar fascia. Above, it is fixed to the last rib, and is 

 thickened to form the lateral lumbo-costal arch^ whilst inferiorly 

 it blends with the ilio- lumbar ligament. The quadratus 

 lumborum muscle, therefore, is enclosed in a sheath formed 

 anteriorly by the anterior lamella of the lumbar fascia, and 

 posteriorly by the middle lamella of the lumbar fascia (Fig. 

 114, p. 249). 



Fascia covering the Psoas and Iliacus. One continuous 

 membranous sheet of fascia covers the anterior surfaces of 

 the psoas and iliacus muscles on each side. Above the level 

 of the crest of the ilium, where it is in relation only to the 

 psoas, it is thin and narrow. There it is attached laterally 

 to the fascia covering the quadratus lumborum, whilst medially 



