THE ILIAC REGION 505 



The Psoas magnus (m. psoas major) (Fig. 381) is a long fusiform muscle placed 

 on the side of the lumbar region of the vertebral column and the margin of the pelvis. 

 It arises from the front of the bases and lov er borders of the transverse processes 

 of the lumbar vertebrae by five fleshy slips; also from the sides of the bodies and 

 the corresponding intervertebral substances of the last thoracic and all the lumbar 

 vertebrae. The muscle is connected to the bodies of the vertebra? by five slips; 

 each slip is attached to the upper and lower margins of two vertebra?, and to the 

 intervertebral substance between them, the slips themselves being connected by 

 the tendinous arches which extend across the constricted part of the bodies, and 

 beneath which pass the lumbar arteries and veins and filaments of the sympathetic 

 cord. These tendinous arches also give origin to muscle fibres, and protect 

 the bloodvessels and nerves from pressure during the action of the muscle. The 

 first slip is attached to the contiguous margins of the last thoracic and first lumbar 

 vertebrae; the last to the contiguous margins of the fourth and fifth lumbar ver- 

 tebrae, and to the intervertebral substance. From these points the muscle descends 

 across the brim of the pelvis, and, diminishing gradually in size, passes beneath 

 Poupart's ligament, and terminates in a tendon which, after receiving nearly t the 

 whole of the fibres of the Iliacus, is inserted into the lesser trochanter of the femur. 



Relations. In the lumbar region, by its anterior surface, which is placed behind the peri- 

 toneum, the Psoas magnus is ih relation with the fascia which covers it, with the ligamentum 

 arcuatum internum, the kidney, Psoas parvus, renal vessels, ureter, spermatic vessels, genito- 

 femoral nerve, and the colon. In many cases the vermiform appendix rests uponthe right Psoas 

 muscle (page 506). By its posterior surface, witlTthetransverse processes of"fhe lumbar veF- 

 tetme and the Quadratus lumborum muscle, from which it is separated by the anterior lamella 

 of the lumbar fascia. The lumbar plexus is situated in the posterior part of tire substance of 

 the muscle. By its inner side the muscle is in relation with the bodies of the lumbar vertebrw, 

 the lumbar arteries, the ganglia of the sympathetic cord, and their branches of communication 

 with the spinal nerves; the lumbar nodes; the inferior vena cava on the right and the aorta 

 on the left side, and along the brim of the pelvis with the external iliac artery. In th^high 

 it is in relation, superficially, with the fascia lata; deeply, with the capsulai* ligament of the hip, 

 from which it is separated by a synovial bursa (bursa iliopectinea) , which frequently commuhi- 

 cates with the cavity of the joint through an opening of variable size; between the tendon and. 

 part of the lesser trochanter is the bursa iliaca subtendinea; by its inner border, with the rectin*k 

 and internal circumflex artery, and also with the femoral artery, which slightly overlaps il^by 

 its outer border, with the femoral nerve and Iliacus muscle. 



The Psoas parvus (m. psoas minor) (Fig. 381) is a long, slender njijtecle placed 

 in front of the Psoas magnus. It arises from the sides of the Us><cfies of the last 

 thoracic and first lumbar vertebra? and from the interve^ebraJ^slibstance between 

 them. It forms a small, flat, fleshy bundle, which terminates'in a long flat tendon 

 inserted into the iliopectineal eminence, and, by its cfpt'er border, into the iliac 

 fascia. This muscle is often absent, and is smnetimes double. 



The Iliacus (TO. iliacus) (Fig. 381) 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 iliolumbar liga- 

 ment and base of the sacrum; in front, from the anterior superior and anterior 

 inferior spinous processes of the ilium, from the notch between them. The 

 fibres converge to be inserted into the outer side of the tendon of the Psoas, some 

 of them being prolonged and attached to the shaft of the femur for about an inch 

 below and in front of the lesser trochanter. 1 The most external fibres are inserted 

 into the capsule of the hip-joint. 



Relations. Within the abdomen, by its anterior surface, with the iliac fossa, which separates 

 the muscle from the peritoneum, and with the external cutaneous nerve; on the right side, 

 with the cecum; on the left side, with the pelvic colon; by its posterior surface, with the iliac 

 fossa; by its inner border, with the Psoas magnus and femoral nerve. In the thigh, it is in 



1 The Psoas and Iliacus are often regarded as a single muscle the Iliopsoas having two heads of origin and 

 a single insertion. 



