764 ' A MANUAL OF ANATOMY 



the inferior vena cava, and with the common iliac veins or some 

 of their tributaries. They therefore form important channels 

 by which a considerable quantity of blood is returned from the 

 lower limbs and abdominal wall in cases of obstruction of the 

 inferior vena cava. 



The upper left, or accessory, azygos vein will be found described 

 in connection with the thorax. 



FasciaB of the Posterior Abdominal Wall — Iliac Fascia. — ^This 

 fascia covers the iliacus and psoas magnus muscles. Above the 

 level of the iliac crest it is related only to the psoas magnus, and 

 the part covering that muscle is spoken of as the psoas sheath. 

 Superiorly it forms the internal arcuate ligament, which extends 

 between the tip of the first lumbar transverse process and the side 

 of the body of that vertebra. Internally it is attached to (a) the 

 intervertebral discs and contiguous margins of the bodies of the 

 lumbar vertebrae, and (h) the fibrous arches over the lumbar vessels 

 opposite the centre of each lumbar body. Externally, near the tips 

 of the lumbar transverse processes, it blends with the anterior 

 lamina of the lumbar aponeurosis which covers the quadratus 

 lumborum. Below the level of the iliac crest the iliac fascia covers 

 the iliacus as well as the psoas magnus. This part of it is known as 

 the fascia iliaca, and it passes uninterruptedly from the iliacus on to 

 the psoas magnus. Externally it is attached to the anterior two-thirds 

 of the iliac crest immediately within its inner lip, and internally 

 to the ala of the sacrum and the iliac portion of the ilio-pectineal 

 line. Inferiorly it is disposed in the following manner : along the 

 outer half of Poupart's ligament on its deep aspect the fascia is 

 firmly attached to that ligament, and joins the fascia transversalis, 

 the two constructing a canal which contains the first part of the deep 

 circumflex iliac artery. Opposite the external iliac vessels the 

 fascia passes downwards behind them and Poupart's ligament to 

 form the posterior wall of the crural sheath. Internal to the 

 external iliac vessels it is continuous with the pubic lamina of the 

 fascia lata, as that covers the upper part of the pectineus. From 

 the point of junction between the iliac fascia and the pubic fascia 

 lata an intermuscular septum (ilio-pectineal) passes backwards 

 between the pectineus and the psoas magnus to be attached to the 

 ilio-pectineal eminence and the front of the capsular ligament of 

 the hip- joint. 



The importance of the iliac fascia has reference to the course taken by 

 pus in cases of lumbar (psoas) abscess. The pus cannot pass outwards over 

 the quadratus lumborum without bursting through the psoas sheath, because 

 the psoas sheath is bound down to the anterior wall of the sheath of the 

 quadrajtus lumborum at the outer border of the psoas muscle. It cannot 

 pass across the vertebral column on account of the attachments of the psoas 

 sheath in that situation. The usual course, therefore, taken by the pus is 

 to diffuse itself downwards within the psoas sheath. On reaching the iliac 

 fossa it may diffuse itself outwards beneath the iliac fascia as that covers 

 the iliacus muscle, but it cannot enter the pelvic cavity on account of the 

 attachment of the iliac fascia to the pelvic brim, unless it bursts through the 

 psoas sheath. Subsequently the pus usually treks along the psoas magnus 



