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.
Action.—Assists the pectoralis minor.
B. Muscles of the Wall of the Thorax.
—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.
Relations.—Outer surface with the serratus anterior (i), the latissimus dorsi ([Fig. 68], m), and the rhomboideus. Inner surface with the external intercostals ([Fig. 73], m), the iliocostal ([Fig. 69], h), the longissimus dorsi ([Fig. 69], f), the spinalis dorsi ([Fig. 69], g), and the splenius ([Fig. 73], b).
Action.—Draws the ribs craniad.
M. serratus posterior inferior ([Fig. 73], n).—The serratus posterior inferior is a thin muscle lying caudad of the serratus posterior superior (l) and sometimes overlying the caudal end of the latter.
Origin by four or five heads from the last four or five ribs. In some specimens only three heads may be present. The separate bundles pass dorsocaudad and unite to form a continuous sheet which ends in a continuation of the aponeurosis of the serratus posterior superior (l).