_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.
_Insertion._--It ends in a flat tendon which in passing is connected by a strong fascia with the tendon of the latissimus (Fig. 65, _q_). It passes along the inner surface of the pectoralis minor (_o_) to be inserted with its cranial fibres near the ventral border of the bicipital groove.
_Relations._--Outer surface with the cutaneus maximus at its medial end, with the pectoralis minor (_o_) at its distal end. Inner surface with the external oblique (Fig. 68, _p_), the rectus abdominis (Fig. 73, _k_), and a mass of fat in the axilla. Borders free. Some of the fibres of the cutaneus maximus are attached to its outer surface.
=M. serratus posterior superior= (Fig. 73, _l_).--A thin sheet of muscle and tendon beneath the serratus anterior (_i_) on the dorsal part of the thorax and neck.
_Origin_ by fleshy slips from the outer surfaces of the first nine ribs just ventrad of their angles. The origin may extend as far as the tenth or eleventh ribs. The first slip is usually delicate. The fibres are directed dorsad and craniad and unite to form a continuous sheet. This ends along a longitudinal line opposite the vertebral transverse processes in the aponeurosis which covers the longissimus dorsi and other muscles in this region. Its insertion is into the median dorsal raphe between the axial spinous process and the tenth thoracic spinous process.