THE THIGH. 505 



of the hip-joint. The fibres converge to be inserted into the outer side of the 

 tendon of the Psoas, some of them being prolonged into the oblique line which 

 extends from the lesser trochanter to the linea aspera. 1 



Relations. Within the pelvis : by its anterior surface, with the iliac fascia, 

 which separates the muscle from the peritoneum, and with the external cutaneous 

 nerve ; on the right side, with the caecum ; on the left side, with the sigmoid 

 flexure of the colon ; by its posterior surface, with the iliac fossa ; by its inner 

 border, with the Psoas magnus and .anterior crural nerve. In the thigh, it is in 

 relation, by its anterior surface, with the fascia lata. Rectus. and Sartorius; 

 behind, with the capsule of the hip-joint, a synovial bursa common to it and the 

 Psoas magnus being interposed. 



Nerves. The Psoas magnus, and the Psoas parvus when it exists, are supplied 

 by the anterior branches of the lumbar nerves ; the Iliacus by the anterior crural. 



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

 upon the pelvis, and. at the same time, rotate the femur outward, from the 

 obliquity of their insertion into the inner and back part of that bone. Acting 

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

 portion of the spine and pelvis forward. They also serve to maintain the erect 

 position, by supporting the spine 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. 



Surgical Anatomy. In the iliac fascia there is no definite septum between the portions of 

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

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

 as it is very apt to do. the matter is contained in an osseo-fibrous 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. 



-s within the sheath of the Psoas muscle (Psocts abscess) is generally due to tubercular 

 caries of the bodies of the lower dorsal and lumbar vertebrae. When the disease is in the dorsal 

 region, the matter tracts down the posterior mediastinum, in front of the bodies of the vertebrae, 

 and. passing beneath the ligamentum arcuatuni 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 



- sheath : i2' a dilated sac in the iliac fossa ; (3) a constricted neck under Poupart's liga- 

 ment : and 4 a dilated sac in the upper part of the thigh. When the lumbar vertebrae are 

 the seat of the disease, the matter finds its way directly into the substance of the muscle. The 

 muscular fibres are destroyed, and the nervous 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 matter may leave the muscle above the crest of the ilium, and, tracking backward, 

 may point in the loin nonpar 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 saero-sciatic notch, discharge itself on the back of the thigh ; or it may open into the 

 bladder or find its way into the perinasum. 



THE THIGH. 

 Anterior Femoral Region. 



Tensor vaginae femoris. Vastus externus. 



Sartorius. Vastus internus. 



Rectus. Crureus. 

 Subcrureus. 



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

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

 a vertical incision from the centre of this, along the middle of the thigh to below the knee-joint; 

 and a transverse incision from the inner to the outer side of the leg, at the lower end of the ver- 

 tical incision. The flaps of integument having been removed, the superficial and deep fasciae 



1 The Psoas and Iliacus are sometimes regarded as a single muscle, the Hio-psoag, having two 

 heads of origin and a single insertion. 



