Insertion ([Fig. 81], e) along a line which begins at the infraspinatus fossa of the great tuberosity, and runs parallel to the deltoid ridge until it reaches the pectoral ridge at the junction of the second and third fourths of the humerus and then continues in the direction of the pectoral ridge as far as the junction of the third and fourth fourths of the humerus. Some of its fibres may pass caudad of the biceps and be inserted with the epitrochlearis. Into the part of the line which is parallel to the deltoid ridge the muscle is inserted by a flat tendon; into the remainder of the line it is usually inserted directly by muscle-fibres, though at its caudal end its insertion may again be tendinous.
Relations.—Outer surface with the cutaneus maximus, the outer layer of the pectoralis major ([Fig. 65], l′), the pectoantibrachialis (m), and the clavobrachial (k). Inner surface with the pectoralis minor (o), the proximal end of the humerus, the coracobrachialis ([Fig. 77], f), and the supraspinatus ([Fig. 77], d) at the insertion of the latter. At the cranial part of its origin it touches the sternomastoid ([Fig. 65], g) and sternohyoid ([Fig. 65], e).
Action.—Draws the arm mediad and turns the foot forward.
M. pectoralis minor, or entopectoralis ([Fig. 65], o).—This is a fan-shaped mass of fibres, flat but thicker than the pectoralis major.
Origin from the lateral half of the first six divisions of the body of the sternum and sometimes from the xiphoid process. The fibres are divisible into several bundles which vary in extent and distinctness and are sometimes described as separate muscles. They pass craniolaterad and converge so that the line of insertion is about one-half as long as that of the origin.
Insertion ([Fig. 81], d) into the humerus along a line which forms the ventral border of the bicipital groove at the proximal end of the bone, passes thence onto the pectoral ridge and continues in the direction of the pectoral ridge nearly as far as the middle of the length of the humerus. The cranial and caudal fibres are inserted by means of a thin tendon; the middle fibres directly. The cranial border of the tendon of insertion is continued as a thin tendon to the coracoid process; it is closely united with the insertion of the supraspinatus.
Relations.—By its outer surface with the pectoralis major ([Fig. 65], l) over its cranial half; with the cutaneus maximus, latissimus dorsi ([Fig. 65], q), and integument over its caudal half. By its inner surface with the xiphihumeralis ([Fig. 65], p), rectus abdominis ([Fig. 73], k), and a mass of fat in the axilla. The tendon of the xiphihumeralis is also connected with its inner surface near its insertion. Its cranial border is free. Its caudal border is in relation at its medial end with the xiphihumeralis, at its lateral end with the tendon of the latissimus dorsi ([Fig. 65], q).
Action.—Draws the arm toward the middle line.
M. xiphihumeralis ([Fig. 65], q).—A long, thin, narrow muscle which may be considered as part of the pectoralis minor.
Origin a median raphe along the xiphoid process or at an angle to the median line on the rectus abdominis muscle. It passes craniad, becoming gradually smaller, and about two centimeters from its insertion ends in a thin tendon.