348 THE MUSCLES 



2. ILIACUS 



The iliacus — named from its attaclimeiit to the iUum — is a thick, triangular 

 sheet. 



Origin. — (1) The ujiper surface of the ala of the sacrum; (2) the front of the 

 ilio-lumbar, lumbo-sacral, and anterior sacro-iliac hgaments; (3) the upper and 

 outer half of the venter of the ilium; (4) the origin of the upper tendon of the 

 rectus femoris and tlie ilio-femoral ligament near the anterior inferior spine of the 

 ilium. 



Insertion. — (1) The outer surface of the tendon of the psoas, through which 

 it is attached to the back of the lesser trochanter of the femur; (2) the upper and 

 back part of the shaft of the femur in a line about one inch (2-5 cm.) long leading 

 downwards from the lesser trochanter. 



Structure. — Arising by fleshy fibres, the muscle converges in a fan-shape down- 

 wards and inwards, and its fil)res enter the outer surface of the tendon of the psoas 

 muscle from about tAvo inches (5 cm.) above Poupart's ligament to its insertion. 

 The lowest fibres are also continued, still fleshy, into their insertion on the l)ack 

 part of the shaft of the femur. 



Nerve-supply. — From the lumbar plexus (through the second and third 

 lumbar nerves) Ijy the anterior crural nerve, which gives branches to its anterior 

 surface about the middle of its inner border. 



Action. — Similar to that of the psoas, as a flexor of the thigh; and acting from 

 the femur as a fixed point, it will draw forwards and flex the pelvis upon the thigh. 



Relations. — The iliac fascia in front separates it from the peritoneum and 

 intestines. The profunda femoris artery and several nerves from the luml^ar plexus 

 lie upon it. On its inner side lies the psoas. After passing under Poupart's 

 ligament, it is crossed by the sartorius, and behind lie the rectus femoris and the 

 capsule of the hip-joint. 



Variations. — A small detached muscle occasionally arises from the anterior inferior spine, and 

 is inserted into the lower part of the anterior intertrochanteric line, or the ilio-femoral ligament. 



Psoas Parvus 



The psoas parvus — a small muscle, only occasionally present, named from its position in the 

 loins and its small size — is fusiform and somewhat flattened. 



Origin. — The side of the intervertebral disc between the last thoracic and the first lumbar 

 vertebra and the adjacent borders of the bodies of these vertebrae. 



Insertion. — The ilio-pectineal line. 



Structure. — Arising fleshy, the fibres converge and are inserted in a somewhat jienniform 

 manner into the back and inner surface of a tendon which appears about two inches below the 

 origin of the muscle upon its outer and anterior aspect, and becomes free about the level of the 

 fifth lumbar vertebra. The tendon, a narrow fibrous band, lies ujwn the inner aspect of the psoas 

 niagnus on the brim of the pelvis, and expands at its lower extremity to be attached along the 

 ilio-jH'ctineal line and the ilio-pubal ridge. 



Nerve-supply. — By small filaments from the first nei-ve of the lumbar plexus. 



Action. — To flex the pelvis upon the thorax; or, taking the pelvis as a fixed point, it will 

 flex the lower i)art of the thoracic spine as well as the lumbar spine upon the pelvis. It is a 

 muscle which is well developed in some animals, having for its function the drawing forwards of 

 the lower part of the pelvis, accompanied by the arching of the lumbar spine which is seen when 

 they are running swiftly. 



Relations.— In front, the iliac fascia, peritoneum, ligamentum arcuatum internum, intestines, 

 renal vessels, ureter, external iliac vessels, etc. Behind and externally, the psoas magnus. 



Iliac Fascia 



Investing the abdominal portion of the ilio-psoas is a strong membrane, called 

 the iliac fascia, which is attached to the crest of the ilium externally, and inter- 

 nally to the posterior part of the ilio-pectineal line which forms the brim of the 

 pelvis. 



