624 



HUMAN ANATOMY. 



The psoas magnus appears to be formed by the union of a hyposkeletal trunk muscle with 

 a femoral muscle, the remaining portions of which are represented by the iliacus and pectineus. 

 It is interesting to note in this connection that in those mammaUa in which the quadratus lum- 

 borum is well developed the psoas magnus is correspondingly weak, and vice versa. 



The psoas parvus or 



Fig sqS minor ( Fig. 598 ) is a long, 



^ fiat muscle which lies upon 



the ventral surface of the 

 - _= psoas magnus, represent- 



ing a separated portion of 

 it, and is present in some- 

 thing over 50 per cent, of 

 cases. It arises from the 

 bodies of the last thoracic 

 and first lumbar vertebrae 

 and is inserted into about 

 the middle of the ilio-pec- 

 tineal line (linea termina- 

 lis) of the pelvis. 



External 

 arcuate ligament 



XII rib 



Psoas 

 par\'us 



Quadratus 

 lumborum 



Psoas 

 magnus 



Crest ot 

 ilium 



Iliacus. 



Anterior 

 superior spine 

 of ilium 



Gluteus medius' 



Tensor fasciae - 

 latae 



Lesser^ 

 trochanter 



Internal 

 arcuate ligament 



Ti-Pyriformis 



S>niphysis 

 pubis 



Obturator 

 externus 



Adductor 

 longus, cut 



2. Iliacus (Fig. 598). 



Attachments. — 



The iliacus arises from 

 about the upper half of 

 the anterior surface of 

 the ilium. Its fibres 

 converge downward to 

 form a common tendon 

 with the psoas major, 

 which is inserted into 

 the lesser trochanter of 

 the femur. 



Nerve-Supply. — 

 By the anterior crural 

 nerve from the second, 

 third, and fourth lum- 

 bar nerves. 



Action. — To flex 

 the thigh and rotate it 

 slightly inward ; when 

 the thigh is fixed, to 

 flex the pelvis and trunk 

 upon the femur. 



Relations. — The 

 iliacus covers the pos- 

 terior wall of the false 

 pelvis, and ^ipon the 

 right side has resting 

 upon it the caecum and 

 on the left side the 

 sigmoid colon. It is 

 crossed obliquely by 

 the external cutaneous and the anterior crural nerves ; its inner border is covered 

 by the psoas magnus. It passes beneath Poupart's ligament external to the psoas 

 magnus, its relations in the thigh being identical with those of that muscle. 



Variations. — The iliacus and psoas magnus are not infrequently extensively united, and 

 the two muscles, together with the psoas parvus, when this is present, are frequently spoken of 

 as the tn. ilio-psoas. The fibres of the iliacus which arise from the posterior superior spine 

 of the ilium are often separated from the rest of the muscle to form an iliacus minor, which is 

 inserted into the capsule of the hip-joint or into the anterior intertrochanteric line. 



The Iliac Fascia. — This fascia is a strong sheet of connective tissue which 

 covers the entire ilio-psoas. Above it is attached to the internal arcuate ligament of 



—Pectineus, cut and 

 turned down 



— ^Adductor magnus 



Deep dissection of posterior body-wall and iliac fossa of right side. 



