494 DISSECTION OF THE ABDOMEN. 



Action. The iliacus flexes the hip-joint with the psoas when the femur 

 is movable, and bends forwards the pelvis when the limb is fixed. In 

 consequence of its union with the psoas, the two are described as the flexor 

 ot the hip-joint by Theile. 



The QUADRATUS LUMBORUM (fig. 171 G ) is a short thick muscle be- 

 tween the crest of the hip-bone and the last rib. About two inches wide 

 inferiorly, it arises from the ilio-vertebral ligament, and from the iliac 

 crest of the hip-bone behind, and an inch outside that band. The fibres 

 ascend to be inserted by distinct fleshy and tendinous slips into the apices 

 of the transverse processes of the four upper, or all the lumbar vertebras ; 

 and into the body of the last dorsal vertebra, and the lower border of the 

 last rib for a variable distance. 



This muscle is encased in a sheath derived from the fascia lumborum. 

 Crossing the surface are branches of the lumbar plexus, together with the 

 last dorsal nerve and its vessels. Beneath the quadratus is the mass of 

 the erector spinas muscle. 



Action. Both muscles keep straight the spine (one muscle antagonizing 

 the other) ; and by fixing the last rib they aid in the more complete con- 

 traction of the diaphragm. 



One muscle will incline laterally the lumbar part of the spine to the 

 same side, and depress the last rib. 



Fascia of the quadratus. Covering the surface of the quadratus is a 

 thin membrane, which is derived from the hinder aponeurosis of the trans- 

 versalis abdominis (fascia lumborum, p. 357) ; it passes in front of the 

 quadratus to be fixed to the tips and borders of the lumbar transverse pro- 

 cesses, to the ilio-lumbar ligament below, and to the last rib above. This 

 fascia forms the thickened band called ligamentum arcuatum externum, 

 to which the diaphragm is connected. 



Fascia of the iliacus and psoas. A fascia covers the two flexor muscles 

 of the hip-joint, and extends in different directions as far as their attach- 

 ments. Over the iliacus muscles the membrane is thickest; and a strong 

 accession is received from the tendon of the small psoas. Its disposition 

 at Poupart's ligament, and the part that it takes in the formation of the 

 crural sheath, have been before explained (p. 428). 



Opposite the pelvis the membrane is inserted into the brim of that 

 cavity for a short distance, and into the hip bone along the edge of the 

 psoas. Opposite the spinal column it becomes thin, and is fixed on the 

 one side to the lumbar vertebras and the ligamentum arcuatum internum, 

 but is blended on the other with the fascia on the quadratus. The fascia 

 should be divided over the psoas on the left side, and reflected towards the 

 brim of the pelvis. 



Dissection. The student is now to clean the lymphatic glands lying 

 along the vertebras, and to trace upwards some lymphatic vessels to the 

 thoracic duct. 



To show the origin of the duct, the diaphragm is to be divided over the 

 aorta, and its pillars are to be thrown to the sides ; a piece may be cut out 

 of the aorta opposite the first lumbar vertebra. The beginning of the duct 

 (chyli receptaculum), and of the vena azygos, may be well seen ; and the 

 two may be followed upwards into the thorax. 



On the left side the student may trace the splanchnic nerves and the 

 small vena azygos through the pillar of the diaphragm ; and may show the 

 trunk of the sympathetic nerve entering the abdomen beneath the arch 

 over the psoas muscle. 



