346 THE MUSCLES 



the pectineus muscle which lies beneath it, and with that muscle it flips beneath the 

 femoral vein and the sheath of the vessels to be attached to the ilio-jiectineal line. 

 This internal division is called the pubic portion of the fascia lata. The deep 

 layer of the superficial fascia stretches across the opening, and is firmly attached to 

 the edge of the falciform process. From the numerous openings which give passage 

 to the vessels and lymphatics, it is here called the cribriform fascia {cribrumhemg 

 the Latin for a sieve). 



MUSCLES OF THE FRONT OF THE THIGH 



In front of the thigh there is a group of four muscles, the chief function of which 

 is to flex the hip-joint. Two of these muscles arise within the abdomen, and two 

 from the margin of the innominate bone. The two Avhich come from within the 

 abdomen are the psoas and iliacus, and they act together as one muscle, and have 

 been described as such under the name of the ilio-psoas. The third and fourth are 

 the sartorius and pectineus. 



1. PSOAS 



The psoas, or psoas magnus — named from the Greek word (}'""■, meaning the 

 muscles of the loins — is thick, rounded, and fusiform. 



Origin. — Inner part, by five processes which arise from (1) the sides of the 

 intervertebral cartilages which intervene between the bodies of the last thoracic and 

 the five lumbar vertebme; and (2) the adjacent part of the sides of the bodies of 

 these vertebrse; and between these processes from (3) tendinous arches which bridge 

 over the sides of the bodies of the first four lumbar vertebrae. Outer part, from the 

 lower border and the front of the transverse processes of all the luml:»ar vertebra?. 



Insertion, — The lower and back part of the lesser trochanter of the femur. 



Structure. — With the exce}>tion of the small tendinous arches which span the 

 sides of each of the four upper luml^ar vertebrae from its upper to its lower border, 

 and which give passage to the lumbar vessels, the whole origin of the muscle is 

 fleshy. The fibres pass downwards and forwards in penniform fashion, but with a 

 slight convergence, to the inner side of the tendon, which, beginning in the interior 

 of the muscle about the level of the crest of the ilium, becomes free upon its outer 

 and posterior surface a short distance above Poupart's ligament, while upon its 

 inner surface it receives fibres down to its insertion. The muscle, having hitherto 

 run in a downward, forward, and slightly outward direction, changes its course at 

 Poupart's ligament, and passes downwards and backwards to be attached to the 

 lesser trochanter of the femur. In its passage along the brim of the pelvis and 

 over the lower part of the iliac fossa, the tendon upon its outer aspect begins to 

 receive the insertion of the iliacus muscle. Between the tendon and the capsule of 

 the hip-joint which is in close connection with it, is placed a bursa which frequently 

 communicates through an opening in the capsule with the interior of the hip-joint. 



Nerve-supply. — From the anterior primary branches of the second and third 

 lumbar nerves l)y filaments which are given ofi" from the lumliar plexus whilst it is 

 passing through the muscle. 



Action. — The p.soas is a powerful flexor of the thigh upon the pelvis, e.g. in 

 walking, ruiming, or going upstairs. The change in the direction of the tendon 

 after crossing the horizontal ramus of the pubes makes its insertion nearly per])en- 

 dicular to the axis of the femur. The psoas therefore acts with less mechanical 

 disadvantage than is usual with the muscles of the limbs. It has been sometimes 

 described as an external rotator of the hip; and its insertion into the lesser 

 trochanter at the inner side of the femur would appear to favour this view. In 

 order to determine whether it has this action, it is necessary to ascertain whether the 

 line of the tendon of the psoas lies internal or external to the axis of rotation. This 

 axis may ])e found by drawing a straight line fi-om the centre of the head of the 

 fenuir to the centre of gravity of the lower limV), which, when. the knee is extended, 

 will be about the middh^ of the intercondylar noteh. By reference to the articulated 

 skeleton it will be seen tliat on account of the position of the lesser trochanter in 



