=Tuberosities.=--Projecting beyond the acromion (the arm hanging by the side), we can feel, through the fibres of the deltoid, the upper part of the humerus. It distinctly moves under the hand when the arm is rotated. It is not the head of the bone which is felt, but the tuberosities, the greater externally, the lesser in front. These tuberosities form the convexity of the shoulder. When the arm is raised, this convexity disappears; there is a slight depression in its place. The head of the bone can be felt by pressing the fingers high up in the axilla. The absence of this prominence formed by the upper part of the humerus under the deltoid, and the presence of a prominence low in the hollow of the axilla, or in front, below the coracoid process, or behind, on the back of the scapula, bespeak dislocation of the head of the bone. In examining obscure injuries about the shoulder, it is worth remembering that, in the normal relation of the bones, and in every position, the great tuberosity faces in the direction of the external condyle. The head of the bone faces very much in the direction of the internal condyle. It is worth remembering also that the upper epiphysis of the humerus includes the tuberosities; and that it does not unite by bone to the shaft, till about the 20th year. By making deep pressure in front of the shoulder, when the arm is pendent and supine, we can feel the bicipital groove. It looks directly forwards, and runs in a line drawn vertically downwards through the middle of the biceps to its tendon at the elbow. We should be aware of this, lest it be mistaken for a fracture. 132. =Coraco-acromial ligament.=--Under the anterior fibres of the deltoid, we can distinctly feel the position and extent of the coraco-acromial ligament. A knife, passed vertically through the middle of it, goes at once into the shoulder joint and strikes the bicipital groove with the tendon, a point to be remembered in excision. In persons of an athletic build the triangular form and beautiful structure of the deltoid become conspicuous when the muscle is in action. The depression on the outer side of the arm, indicating its insertion, is the place selected for issues or setons. The arm being held up by an assistant, the anterior and posterior borders of the relaxed deltoid admit of being raised so that in amputation at the shoulder the knife can be introduced beneath the muscle to make the flap.