_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.
_a_, M. frontoscutularis; _b_, M. masseter; _c_, M. sternomastoideus; _d_, M. clavotrapezius; _e_, M. clavobrachialis; _f_, M. levator scapulæ ventralis; _g_, M. acromiodeltoideus; _h_, M. acromiotrapezius; _i_, M. spinodeltoideus; _j_, M. spinotrapezius; _k_, caput longum of M. triceps brachii; _l_, caput laterale of M. triceps brachii; _m_, M. latissimus dorsi; _n_, M. xiphihumeralis; _o_, M. pectoralis minor; _p_, M. obliquus abdominis externus; _q_, M. sartorius; _r_, M. tensor fasciæ latæ; _s_, M. caudofemoralis; _t_, M. biceps femoris; _u_, M. semitendinosus; _v_, M. extensor caudæ lateralis; _w_, M. abductor caudæ externus; _x_, M. flexor caudæ longus; _y_, lumbodorsal fascia, superficial layer; _z_, fascia lata. 1, parotid gland; 2, submaxillary gland.]
_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 scapulæ, and splenius. Near its origin its caudal border touches the outer surface of the spinotrapezius (_j_). Its cranial border is overlaid near its insertion by the levator scapulæ ventralis (_f_) and is closely related to the caudal border of the clavotrapezius (_d_) near its origin.