133. =Axilla.=--The anterior border of the axilla, formed by the pectoralis major, follows the line of the fifth rib. In counting the ribs, or in tapping the chest, it is worth remembering that the highest visible digitation of the serratus magnus is attached to the sixth rib. The angle of the digitation is directed forwards, and corresponds to the upper edge of the rib. The second visible digitation corresponds to the seventh rib; the interval between these digitations, therefore, corresponds to the sixth intercostal space--a convenient place for tapping the chest. (38) In the normal state no glands can be felt in the axilla. 134. =Axillary artery.=--When the arm is raised to a right angle with the body, and the head of the humerus thereby depressed, the axillary artery is plainly felt beating, and can be perfectly compressed on the inner side of the coraco-brachialis. This muscle stands out in relief along the humeral side of the axilla, and is the best guide to the artery. A line drawn along its inner border--that is, down the middle of the axilla--corresponds with the course of the artery. The depth and form of the axilla alter in different positions of the arm. In the arm raised and abducted the axilla becomes nearly flat; hence this position is always adopted in operations. In opening abscesses in the axilla, the incision should be made midway between the borders, and the point of the knife introduced from above downwards. 135. =Brachial artery.=--When the arm is extended and supinated, a line drawn from the deepest part of the middle of the axilla down the inner side of the biceps to the middle of the bend of the elbow, corresponds with the course of the brachial artery. The artery can be felt and compressed all the way down; but nowhere so effectually as midway, where it lies on the tendon of the coraco-brachialis close to the inner side of the humerus. The only direction to apply the pressure effectually is outwards and a little backwards, else the artery will slip off the bone. The musculo-spiral nerve and superior profunda artery wind round the back of the humerus about its middle, and come to the front of the external condyloid ridge. Thus, for full three inches above the condyles, there is nothing to interfere with operations on the back of the bone, which is here broad and flat. 136. =Bend of elbow.=--At the bend of the elbow, the tendon of the biceps can be plainly felt, as well as the pulsation of the brachial artery close to its inner side, before dividing into the radial and ulnar.