THE ILIAC REGION. 417 



of the sympathetic nerve, and their branches of communication with the spinal 

 nerves ; the lumbar glands ; the vena cava inferior on the right and the aorta on 

 the left side, and along the brim of the pelvis with the external iliac artery. In 

 the thigh it is in relation, in front, with the fascia lata ; behind, with the capsular 

 ligament of the hip, from which it is separated by a synovial bursa, which 

 frequently communicates with the cavity of the joint through an opening of 

 variable size ; by its inner border, with the Pectineus and internal circumflex 

 artery, and also with the femoral artery, which slightly overlaps it : by its outer 

 border, with the anterior crural nerve and Iliacus muscle. 



The Psoas parvus is a long slender muscle placed in front of the Psoas magnus. 

 It arises from the sides of the bodies of the last dorsal and first lumbar vertebrae 

 and from the intervertebral substance between them. It forms a small flat muscular 

 bundle, which terminates in a long flat tendon inserted into the ilio-pectineal 

 eminence, and, by its outer border, into the iliac fascia. This muscle is often 

 absent, and, according to Cruveilhier, sometimes double. 



Relations. It is covered by the peritoneum, and, at its origin, by the ligamentum 

 arcuatum internum ; it rests on the Psoas magnus. 



The Iliacus is a flat, triangular muscle which fills up the whole of the iliac 

 fossa. It arises from the upper two-thirds of this fossa and from the inner margin 

 of the crest of the ilium ; behind, from the ilio-lumbar ligament and base of the 

 sacrum ; in front, from the anterior superior and anterior inferior spinous processes 

 of the ilium, from the notch between them, and by a few fibres from the capsule 

 of the hip-joint. The fibres converge to be inserted into the outer side of the 

 tendon of the Psoas, some of them being prolonged on to the shaft of the femur 

 for about an inch below and in front of the lesser trochanter. 1 



Relations. Within the abdomen : by its anterior surface, with the iliac fascia, 

 which separates the muscle from the peritoneum, and with the external cutaneous 

 nerve; on the right side, with the csecum ; on the left side, with the sigmoid flexure 

 of the colon ; by its posterior surface, with the iliac fossa ; by its inner border, 

 with the Psoas magnus and anterior crural nerve. In the thigh, it is in relation, 

 by its anterior surface, Avith the fascia iata, Rectus, Sartorius, and profurida femoris 

 artery; behind, with the capsule of the hip-joint, a synovial bursa common to it 

 and the Psoas magnus being interposed. 



Nerves. The Psoas magnus is supplied by the anterior branches of the second 

 and third lumbar nerves ; the Psoas parvus, when it exists, is supplied by the 

 anterior branch of the first lumbar nerve ; and the Iliacus by the anterior 

 branches of the second and third lumbar nerves through the anterior crural. 



Actions. The Psoas and Iliacus muscles, acting from above, flex the thigh 

 upon the pelvis. Acting from below, the femur being fixed, the muscles of both 

 sides bend the lumbar portion of the spine and pelvis forward. They also serve to 

 maintain the erect position, by supporting the spine and pelvis upon the femur, 

 and assist in raising the trunk when the body is in the recumbent posture. 



The Psoas parvus is a tensor of the iliac fascia. 



Surgical Anatomy. In the iliac fascia there is no definite septum between the portions of 

 fascia covering the Psoas and Iliacus respectively, and the fascia is only connected to the subja- 

 cent muscles by a quantity of loose connective tissue. When abscess forms beneath this fascia, 

 as it is very apt to do, the matter is contained in an osseo-fibrous cavity which is closed on all 

 sides within the abdomen, and is open only at its lower part, where the fascia is prolonged over 

 the muscle into the thigh. 



Abscess within the sheath of the Psoas muscle (Psoas abscess) is generally due to tubercular 

 caries of the bodies of the lower dorsal and lumbar vertebrae. When the disease is in the dorsal 

 region, the matter tracts down the posterior mediastinum, in front of the bodies of the vertebrae, 

 and, passing beneath the ligamentum arcuatum internum, enters the sheath of the Psoas muscle, 

 down which it passes as far as the pelvic brim ; it then gets beneath the iliac portion of the fascia 

 and fills up the iliac fossa. In consequence of the attachment of the fascia to the pelvic brim, it 

 rarely finds its way into the pelvis, but passes by a narrow opening under Poupart's ligament 



1 The Psoas and Iliacus are sometimes regarded as a single muscle, the Itio-psoas, having two heads 

 of origin and a single insertion. 



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