After its passage between the quadratus and the adductor magnus, the circumflex artery divides, in the posterior region of the thigh, into an ascending and a descending branch. The former passes upward to the origin of the biceps, semi - membranosus and tendinosus muscles, and to the glutceus maximus ; the latter downward to the former muscles, to the adductor magnus, and to the sciatic nerve. They communicate with the sciatic, the exter nal circumflex, and superior perforating arte ries.
The perforating arteries are three or four in number. They are given off backward by the profunda, below the origin of the circumflex arteries, and are denominated numerically first, second, third, &c. They all pass from the an terior to the posterior region of the thigh' by perforating the adductor magnus, and at times also the adductor brevis, whence their name ; they divide for the most part into ascending and descending branches, and are consumed partly in the supply of that region, and partly in establishing a chain of communications be tween the arteries of the trunk and the main artery at the upper and the lower parts of the thigh.
3. Thefirst perforating artery arises from the profunda immediately below the lesser trochan ter, nearly opposite the lower margin of the pcctinalis : it passes backward, descending a little below the lower margin of the pectinalis, either between it and the upper one of the ad ductor brevis, or through an aperture in the latter muscle : it next perforates the adductor magnus close to the linea aspen, and so gains the posterior region of the thigh, where it divides into two or three large branches, of which one ascends and is distributed to the glutceus maximus, communicating with the glutceal, sciatic, and circumflex arteries ; ano ther descends, supplies the long head of the biceps, the semi-membranosus and semi-tendi nosus, and communicates with the inferior per forating arteries ; and the third runs downward and outward into the vastus externus, through which it descends, communicating at the same time with the external circumflex artery. The artery also gives branches to the sciatic nerve, and, during its passage from the front to the back of the thigh, to the pectinalis and the ad ductors. According to Harrison, " this artery is sometimes a branch of the internal circum flex; its course is nearly parallel to that vessel, and is separated from it by the tendon of the pectinmus muscle, the first perforating artery passing below that tendon, while the circumflex artery runs superior to it."
4. The second perforating artery is generally the largest of those vessels : it arises a short distance below the first, and passes through both the adductors brevis and magnus ; it then divides, like the former, into ascending and de scending branches : the former are distributed to the glutceus maximus, the vastus externus, and the tensor vaginae, likewise anastomosing with the first perforating, the glutceal, sciatic, and circumflex arteries : the latter are distri buted to the biceps, semi-membranosus, and semi-tendinosus, the vastus externus, and the integuments of the back of the thigh, and in osculate with the inferior perforating and with branches of the popliteal artery. The artery also gives branches to the adductor muscles and to the sciatic nerve and the nutritious artery of the femur, which enters a canal to be ob served in the linea aspera, at the junction of the first and second thirds of the thigh, leading obliquely upward into the bone. The second perforating artery at times does not pass through the adductor brevis, but when the first does so, it generally runs inferior to it, perfora ting the adductor magnus only.
5. The third petforating artery is smaller than either of the former, and arises lower down ; according to Harrison, at the upper edge of the adductor longus muscles, it passes through the adductor magnus, and divides in the same manner as the others : its branches are also similarly distributed, and anastomose with the second perforating artery from above, and with branches of the popliteal from below.
When a fourth perforating artery exists, it pursues a similar course and is distributed similarly to the last. The perforating branches of the profunda are subject to much variety with regard to number, size, and precise course and distribution ; so much so that they hardly admit a definite description : the preceding ac count has been taken from a comparison of the most approved authorities with the subject, in order, as far as possible, to embrace their nu merous irregularities.