The Internal Circumflex Artery, usually larger than the external, arises from the posterior and internal part of the profunda. It first sinks, from before backwards, between the pectineus and the tendon of the psoas and iliacus; next between the obturator externus muscle above, and the superior edge of the adductor brevis below; and, lastly, between the lower margin of the quadratus femoris and the upper fibres of the adductor magnus. In this course it winds round the inside of the neck of the femur and capsule of the hip-joint: its termination may be seen by raising the glutaeus maximus. The course of the artery between these layers of muscles and adjacent parts has been thus described by Dr. Harrison:"It is surrounded by a quantity of loose cellular membrane, and is situated in a sort of cavity of a triangular figure, bounded externally by the capsular ligament, by the neck of the femur, and by the psoas and iliac muscles and tendon; superiorly by the obturator externus; and internally by the adductor muscles: this space is covered anteriorly by the pectineus, and partly closed posteriorly by the adductor magnus and quadratus femoris, between which muscles there is a narrow fissure, through which pass the terminating branches of this artery." The branches of the internal circumflex may be classed into the internal, external, ascending, and terminating. The internal branches are distributed to the adductor muscles, and sometimes supply the place of the superficial pudic arteries. The external branch* is small; it passes through the notch in the internal margin of the acetabulum and beneath the transverse ligament, and is then conducted by the ligamentum teres to the head of the femur, which it supplies. The ascending branches supply the pectineus and origin of the adductor longus: on dividing the pectineus, we find them freely inosculating with the branches of the obturator artery; and still deeper there is a trochanteric branch, which ascends in front of the quadratus femoris muscle, to arrive at the digital fossa of the great trochanter: it supplies the muscles inserted in this situation, and inosculates with the sciatic, glutaeal, and external circumflex arteries. On placing the subject on its face and raising the glutaeus maximus muscle, we see the termination of the internal circumflex artery running inwards and backwards along the lower margin of the quadratus femoris muscle, through a space formed between this muscle superiorly, the upper part of the adductor magnus inferiorly, and the root of the trochanter minor externally. Here it supplies the origins of the hamstring muscles, the adductor magnus, and the sciatic nerve, and anastomoses freely with the sciatic and glutaeal arteries.

* In complete fracture of the neck of the femur, within the capsular ligament, this and a similar branch of the obturator are the only direct sources from which the head of the bone can receive blood; and this is one of the reasons assigned by Sir A. Cooper why osseous union does not occur in those cases.

On one occasion M. Roux cut down on this vessel, and tied it; but such an operations will be seldom necessary.