The Adductor magnus is a large triangular muscle, situated on the medial side of the Thigh. It arises from a small part of the inferior ramus of the pubis, from the inferior ramus of the ischium, and from the outer margin of the inferior part of the tuberosity of the ischium. Those fibers which arise from the ramus of the pubis are short, horizontal in direction, and are inserted into the rough line leading from the greater trochanter to the linea aspera, medial to the Glutæus maximus; those from the ramus of the ischium are directed downward and lateralward with different degrees of obliquity, to be inserted, by means of a broad Aponeurosis, into the linea aspera and the upper part of its medial prolongation below. The medial portion of the muscle, composed principally of the fibers arising from the tuberosity of the ischium, forms a thick fleshy mass consisting of coarse bundles which descend almost vertically, and end about the lower third of the Thigh in a rounded tendon which is inserted into the adductor tubercle on the medial condyle of the Femur, and is connected by a fibrous expansion to the line leading upward from the tubercle to the linea aspera. At the insertion of the muscle, there is a series of osseoaponeurotic openings, formed by tendinous arches attached to the Bone. The upper four openings are small, and give passage to the perforating branches of the profunda femoris artery. The lowest is of large size, and transmits the femoral vessels to the Popliteal Fossa. It is supplied by the third and fourth lumbar nerves through the obturator nerve; the Adductor magnus also receives an additional branch from the sacral plexus through the sciatic.

It helps along with the other adductor Muscles to adduct the Thigh powerfully; they are especially used in horse exercise, the sides of the saddle being grasped between the knees by the contraction of these Muscles. In consequence of the obliquity of their insertions into the linea aspera, they rotate the Thigh outward, assisting the external Rotators, and when the limb has been abducted, they draw it medialward, carrying the Thigh across that of the opposite side.