In the dog and the cat it is divided into two parts, anterior and posterior. The first, the more developed, is attached to the internal surface of the inferior extremity of the femur; the second to the internal tuberosity of the tibia. The same arrangement occurs in the ox. In the horse it is inserted into the internal surface of the internal condyle of the femur. The semi-membranosus is an extensor of the thigh when it takes its fixed point at the pelvis; it is also an adductor of the lower limb. If it takes its fixed point below it assists in the action of rearing. It is now necessary for us, especially as regards the horse, to add some indications relative to the exterior forms of the region constituted by the semi-membranosus and semi-tendinosus. These two muscles form, by their union, a surface contour, slightly projecting and of elongated form, which occupies the posterior border of the thigh, the contour corresponding to the region known as the _buttock_, in spite of the fact that none of the gluteal muscles take any part in the structure of this region. But the appearances, to a certain extent, justify the preservation of this name. Indeed, because of the groove which separates the gluteal region of one side from that of the opposite side, and from the position of the anal orifice in the superior part of this groove, we may admit the name which, in hippology, has been given to this part of the thigh. In addition to the reasons just given, and which are justified especially by the position occupied by the muscular mass formed by the union of the two muscles, there is another which, this time, has a relation to a certain detail of form. In the superior part of the convexity, which the gluteal region describes in the greater part of its extent, there is found a more salient point, greatly accentuated in lean animals, due to the presence of the tuberosity of the ischium; it is the _point_ or _angle of the buttock_. At this level, and near the median line, the semi-membranosus, not aponeurotic, but fleshy, and even thicker there than anywhere else, sometimes produces a sharply localized prominence. And as this prominence is situated on the outer side of the anal orifice, the resemblance to a small 'buttock' is still more marked. In lean horses a deep groove separates the mass formed by the semi-membranosus and semi-tendinosus from that of the other muscles of the thigh situated more in front; this groove is known by a name which in this case is remarkably expressive--that of the 'line of poverty.'