506 THE MUSCLES AND FASCIA 



relation, by its superficial surface, with the fascia lata, the Rectus and Sartorius muscles, and 

 the profunda femoris artery; by its deep surface, with the capsule of the hip-joint, a synovial 

 bursa common to it and the Psoas magnus being interposed. 



Nerves. The Psoas magnus is supplied by the anterior branches of the second and third 

 lumbar nerves; the Psoas parvus, when it exists, is supplied by the anterior branch of the first 

 lumbar nerve; and the Iliacus, by the anterior branches of the second and third lumbar nerves 

 through the femoral. 



Actions. The Psoas and Iliacus muscles, acting from above, flex the thigh upon the pelvis. 

 Acting from below, the femur being fixed, the muscles of both sides bend the lumbar portion of 

 the vertebral column and pelvis forward. They also serve to maintain the erect position, by 

 supporting the vertebral column and pelvis upon the femur, and assist in raising the trunk 

 when the body is in the recumbent posture. 



The Psoas parvus is a tensor of the iliac fascia. It assists in flexing the lumbar portion of 

 the vertebral column laterally, the pelvis being its fixed point. 



Applied Anatomy. There is no definite septum between the portions of the iliac fascia 

 covering the Psoas and Iliacus, respectively, and the fascia is only connected to the subjacent 

 muscles by a quantity of loose connective tissue. When an abscess forms beneath this fascia, 

 as it is very liable to do, the pus is contained in an osseofibrous cavity, which is closed on all 

 sides within the abdomen, and is open only at its lower part, where the fascia is prolonged over 

 the muscle into the thigh. 



Abscess within the sheath of the Psoas muscle (Psoas abscess] is generally due to tuberculous 

 caries of the bodies of the lower thoracic or of the lumbar vertebrae. When the disease is in the 

 thoracic region, the pus courses down the posterior mediastinum, in front of the bodies of the 

 vertebras, and, passing beneath the ligamentum arcuatum internum, enters the sheath of the 

 Psoas muscle, down which it passes as far as the pelvic brim; it then gets beneath the iliac 

 portion of the fascia and fills up the iliac fossa. In consequence of the attachment of the fascia 

 to the pelvic brim, it rarely finds its way into the pelvis, but passes by a narrow opening under 

 Poupart's ligament into the thigh, to the outer side of the femoral vessels. It thus follows that 

 a Psoas abscess may be described as consisting of four parts: (1) A somewhat narrow channel 

 at its upper part, in the Psoas sheath; (2) a dilated sac in the iliac fossa; (3) a constricted neck 

 under Poupart's ligament; and (4) a dilated sac in the upper part of the thigh. When the 

 lumbar vertebrae are the seat of the disease, the pus finds its way directly into the substance 

 of the muscle. If a Psoas abscess forms, the muscle fibres are destroyed, and the nerve cords 

 contained in the abscess are isolated and exposed in its interior ; the femoral vessels which lie in 

 front of the fascia remain intact, and the peritoneum seldom becomes implicated. All Psoas 

 abscesses do not, however, pursue this course; the pus may leave the muscle above the crest 

 of the ilium, and, tracking backward, may point in the loin (lumbar abscess}', or it may point 

 above Poupart's ligament in the inguinal region; or it may follow the course of the iliac vessels 

 into the pelvis, and, passing through the great sacrosciatic notch, discharge itself on the back 

 of the thigh; it may open into the bladder or find its way into the perineum, or it may pass 

 down the thigh to the popliteal space or even lower. Strain of the Psoas muscle is not unusual, 

 and induces pain which may be mistaken for appendicitis. The bursa beneath the tendon of 

 the Psoas and Iliacus and the hip-joint or that between the tendon and the lesser trochanter may 

 greatly enlarge and produce pain and disablement. Byron Robinson 1 pointed out that trauma 

 of the Psoas muscle may be an important factor in the etiology of appendicitis, as it may induce 

 periappendicular adhesions which interfere with the circulation of blood and feces. Robinson 

 says, in the previously quoted article, that in 46 per cent, of men and in 20 per cent, of women 

 the appendix rests on the Psoas muscle. 



II. MUSCLES AND FASCIAE OF THE THIGH. 



1. The Anterior Femoral Region. 



Tensor fasciae femoris. Quadriceps 



Sartorius. extensor. 



Rectus femoris. 

 Vastus externus. 



Vastus internus. 

 Crureus. 

 Subcrureus. 



Dissection. To expose the muscles and fasciae in this region, make an incision along 

 Pbupart's ligament, from the anterior superior spine of the ilium to the spine of the os pubis; 



1 Annals of Surgery, April, 1901. 



