PSOAS AND ILTACUS MUSCLES. 493 



The muscle arises from the front of the transverse processes of the 

 lumbar vertebrae; from the bodies and inter vertebral disks of the last 

 dorsal and all the lumbar vertebrae by five fleshy pieces each piece being 

 connected with the intervertebral substance and the borders of two con- 

 tiguous vertebrae, and with tendinous bands over the bloodvessels opposite 

 tire middle of the vertebra. The fibres give rise to a roundish belly, 

 which gradually diminishes towards Poupart's ligament, and ends inte- 

 riorly- in a tendon on the outer aspect, which receives fibres of the iliacus, 

 and passes beneath Poupart's ligament to be inserted into the small tro- 

 chanter of the femur. 



The abdominal part of the muscle has the following connections: In 

 front are the internal arch of the diaphragm, the kidney with its vessels 

 and duct, the spermatic vessels, and the genito-crural nerve, and, near 

 Poupart's ligament, the ending of the external iliac artery. Posteriorly 

 the muscle is in contact with the transverse processes, with part of the 

 quadratus lumborum, and with the innominate bone. 



The outer border touches the quadratus and iliacus; and branches of 

 the lumbar plexus issue from beneath it. The inner border is partly con- 

 nected to the vertebrae, and is partly free along the margin of the pelvis: 

 along the attached part of this border lies the sympathetic nerve, with 

 the cava on the right, and the aorta on the left side ; along the free or 

 pelvic part are the external iliac artery and vein. 



Action. If the femur is free to move it is raised towards the belly; and 

 as the flexion proceeds, the limb is rotated out by the attachment of the 

 muscle to the trochanter minor. The psoas is always combined with the 

 iliacus in flexion of the hip-joint. 



When the lower limbs are iixed the two muscles will draw down the 

 lumbar part of the spine, and bend the hip-joints, as in stooping to the 

 ground. One muscle under the same circumstances can incline the spine, 

 laterally. 



The PSOAS PARVUS (fig. 171, E ) is a small muscle with a long and flat 

 tendon, which is placed on the front of the large psoas, but, is rarely pre- 

 sent. Its fibres arise from the bodies of the last dorsal and first lumbar 

 vertebrae, with the intervening fibro-cartilage. Its tendon becomes broader 

 interiorly, and is inserted into the ilio-pectineal eminence and the brim of 

 the pelvis, joining the fascia over the iliacus muscle. 



Action. If the spine is immovable the two muscles will make tense 

 the pelvic fascia. The pelvis being fixed they may assist in bending the 

 lumbar part of the spinal column. 



The ILIACUS MUSCLE (fig. 171, H ) occupies the iliac fossa on the inner 

 aspect of the hip-bone, and is blended inferiorly with the psoas. It is 

 triangular in form, and has a fleshy origin from the iliac fossa and the 

 ilio-lumbar ligament, from the base of the sacrum, and from the capsule 

 of the hip-joint in front. The fibres pass inwards to the tendon of the 

 psoas, uniting with it even to its insertion into the femur, but some reach 

 separately the femur near the small trochanter. 



Above Poupart's ligament the muscle is covered by the iliac fascia; but 

 over the right iliacus is placed the caecum, and over the left, the sigmoid 

 flexure. Beneath it are the innominate bone and the capsule of the hip- 

 joint; and between it and the grooved anterior margin of the bone, above 

 the joint, is a bursa. The inner margin is in contact with the psoas and 

 the anterior crural nerve. The connections of the united psoas and iliacus 

 below Poupart's ligament are given with the dissection of the thigh. 



