=M. spinotrapezius=, or trapezius inferior (Fig. 68, _j_).--The spinotrapezius (caudal part of the human trapezius) is a flat triangular muscle. _Origin_ from the tips of the spinous processes of all or nearly all the thoracic vertebræ and from the intervening supraspinous ligament. The origin may extend from a point anywhere between the first and fourth spines to any point between the eleventh and thirteenth. _Insertion_ along an S-shaped line (Fig. 76, _k_-_l_) which crosses the tuberosity of the scapular spine and forms an angle with the spine of about forty-five degrees. The line extends on one side onto the fascia covering the supraspinatus muscle, and on the other side onto the fascia covering the infraspinatus, but does not reach the borders of the scapula. The cranial two-thirds of the insertion is by a flat tendon which is broader craniad. _Relations._--Outer surface with the cutaneus maximus, and craniad with the acromiotrapezius (_h_). Inner surface with the latissimus dorsi (_m_) caudad and with the rhomboideus, supraspinatus, and infraspinatus craniad. Caudal border free; cranial border in contact with the acromiotrapezius (_h_). _Action._--Draws the scapula dorsocaudad. =M. acromiotrapezius=, or trapezius superior (Fig. 68, _h_).--The acromiotrapezius (middle part of the human trapezius) is a flat four-sided muscle just craniad of the spinotrapezius, from the median dorsal line to the scapular spine. _Origin_ along the median dorsal line from the spinous process of the axis to a point anywhere between the spinous processes of the first and fourth thoracic vertebræ. Its caudal two-thirds is from a flat tendon which is directly continuous with the muscle of the opposite side and thus bridges the depression between the vertebral borders of the scapulæ. This tendon narrows craniad, and its cranial fourth is attached by a fascia to the spinous processes of the cervical vertebræ. At the cranial border of the muscle the fibres sometimes reach the middle line. The fibres of the muscle run nearly transversely. _Insertion_ (Fig. 76, _h_).--Into the outer surface of the metacromion, the glenoid border of the scapular spine from the metacromion to the tuberosity, and along a line continued for about one centimeter from the tuberosity onto the surface of the spinotrapezius (_j_) at the junction of its muscular and tendinous portions. [Illustration: FIG. 68.--FIRST LAYER OF BODY-MUSCLES, BENEATH THE SKIN AND SKIN-MUSCLES.