766 A MANUAL OF ANATOMY 



erector spinae. The posterior lamina, which is also very strong, 

 is attached to the spinous processes of the lumbar and sacral 

 vertebrae, and the posterior fourth of the outer lip of the iliac crest. 

 It lies behind the erector spinae, at the outer border of which it 

 blends with the middle lamina, and so the muscle is enclosed in a 

 sheath. The posterior lamina is joined by the vertebral aponeurosis, 

 and affords attachment to the latissimus dorsi and serratus posticus 

 inferior. 



Muscles of the Posterior Abdominal Wall — Psoas Magnus — 

 Origin. — (i) The fronts of the transverse processes of the lumbar 

 vertebrae ; (2) the lateral aspects of the intervertebral discs, and 

 of the adjacent borders of the twelfth thoracic, and all the lumbar, 

 vertebrce ; and (3) a series of fibrous arches which cross the lumbar 

 vessels at the centres of the bodies of the lumbar vertebrae. 



Insertion. — The small trochanter of the femur, by a tendon which 

 receives, on its outer side, the greater part of the iliacus. 



Nerve-supply. — ^The lumbar plexus. The branches come more 

 particularly from the anterior primary divisions of the second and 

 third lumbar nerves. 



Action. — Acting from its origin the muscle is a powerful flexor of 

 the thigh upon the pelvis, coming into play in walking, or ascending 

 a stair. Acting from its insertion it is a flexor of the Imnbar 

 portion of the vertebral column upon the pelvis, and of the pelvis 

 upon the thigh, as in the act of stooping. The muscle of one side, 

 acting from its insertion, is capable of producing lateral flexion 

 of the lumbar portion of the vertebral column. 



As the muscle descends close to the pelvic brim the fibres of the 

 iliacus begin to join the outer side of its tendon, and they continue 

 to do so as far as the insertion, thus giving rise to a conjoined 

 muscle known as the ilio-psoas. 



Psoas Parvus. — This muscle is present in man on one or both sides in about 

 45 per cent, of bodies. It arises from the lateral aspect of the intervertebral 

 disc between the twelfth thoracic and first lumbar vertebrae, and from the 

 - -+iofuous borders of their bodies, by means of a small fleshy belly, which is 

 con-cjjiL 01 1*^ 2 inches long. It is then replaced by a long, narrow, flat 

 usually about,, T^^jjjg ^^ -^^ ^g about to take insertion into the middle of the 

 tendon which exp.. , „ the ilio-pectineal eminence, in which latter situation 

 iho-pectmeal line and ^tineal intermuscular septum. 

 It blends with the ilio-pewu ^qj. primary division of the first lumbar aerve. 



The nerve-supply is the ante. ,^ (^^^^ ^^ ^^^ ^^^ l^-^ ^ ^^^ vertebral 

 Acting from its origin the muscu . ^^^^^^^ ^^^^^ f ^.^^ i^s insertion it 

 column, and is a tensor of the psoas rcx.^art of the thoracic portion, of the 

 tends to flex the lumbar portion, and lower i,„^^^gj.ig^i^, ^^^^^ fg g^g^ j^ ^hei 

 vertebral column upon the pelvis. Its chare. .^.^^ ^^^ ^^^ ^f leaping, that! 

 position assumed by saltatory animals preparatoryi ;^ ^^^ vertebral column,] 

 position consisting in a drawing forwards of the pelvl ^^ psoas magnus close 



The psoas parvus lies along the anterior aspect of t^^i*^ ;,.3(jed tendon turns 

 to its inner border, except at the pelvic brim, where its expai..^ 

 to the inner side of that muscle. * 



Iliacus— On;?m.— (I) The upper surface of the ala of i^?^^^^'"""^ 

 (2) the anterior sacro-iliac, ilio-lumbar, and lumbo-sacral life^*^^"! ^ J 

 and (3) the upper half of the iliac fossa, reaching anteriorly,' ^ °^'^ 

 as the anterior inferior iliac s]Mne. 



