116 THE MUSCLES. 
Insertion along an S-shaped line (Fig. 76, &-/) 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 (Z). Inner surface with the 
latissimus dorsi (#z) caudad and with the rhomboideus, supra- 
spinatus, and infraspinatus craniad. Caudal border free; cranial 
border in contact with the acromiotrapezius (4). 
Action.—Draws the scapula dorsocaudad. 
M. acromiotrapezius, or trapezius superior (Fig. 68, 2).— 
The acromiotrapezius (middle part of the human trapezius) is 
a flat four-sided muscle just craniad of the spinotrapezius, cam 
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 vertebrae. 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 scapule. This tendon narrows 
craniad, and its cranial fourth is attached by a fascia to the 
spinous processes of the cervical vertebre. 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, 4).—Into the outer surface of the meta- 
cromion, 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 (7) at the junction of its muscular and tendi- 
nous portions. 
Relations.—Outer surface with the cutaneus maximus, the 
integument and platysma. Inner surface with a mass of fat 
partially covering the rhomboideus; with the occipitoscapularis, 
spinotrapezius, supraspinatus, levator scapula, and_ splenius. 
