Action.—Draws the scapula toward the vertebral column.
M. cleidomastoideus (clavicular portion of the human sternocleidomastoid) ([Fig. 65], h).—A narrow flat muscle between the mastoid process and the clavicle.
Origin from the apex and caudal margin of the mastoid process of the temporal bone, by tendon and muscle fibres. The muscle passes caudad, becoming broader and thinner.
Insertion into the lateral four-fifths of the clavicle within the insertion of the clavotrapezius, and into the raphe which continues laterad of the clavicle.
Relations.—Outer or lateral surface at the caudal end with the clavotrapezius ([Fig. 65], j); further craniad with the depressor conchæ ([Fig. 64], b), the platysma, and the sternomastoid ([Fig. 65], g). Inner or medial surface with the supraspinatus ([Fig. 75], a) caudad, with the mass of fat in the axilla at its middle, with the levator claviculæ ventralis ([Fig. 65], i) and obliquus capitis superior ([Fig. 71], e) craniad.
Action.—Pulls the clavicle craniad when the head is fixed. Turns the head and depresses the snout when the clavicle is fixed.
M. levator scapulæ ventralis, or levator claviculæ ([Fig. 68], f; [Fig. 65], i; [Fig. 72], c, c′, c″) (not usually found in man).
Origin ([Fig. 72], c′, c″) in two parts. (1) By fleshy fibres from the ventral surface of the atlantal transverse process near its caudal border (c′). (2) By a small tendon from the ventral surface of the basioccipital opposite the middle of the length of the bulla tympani (c″) in common with the longus capitis (a). The two heads unite to form a flat band which passes caudoventrad and is inserted ([Fig. 76], f) by a flat short tendon, about eight millimeters broad, into the outer surface of the metacromion along its ventral border, and into the infraspinatus fossa for one or two millimeters distad of that border.
Relations.—Near the insertion the dorsal border overlaps the border of the acromiotrapezius ([Fig. 68], h), and the ventral border is attached by strong fascia to the border of the clavotrapezius ([Fig. 68], d). The outer surface is in relation with the longissimus capitis ([Fig. 73], g), clavotrapezius ([Fig. 68], d), cleidomastoid ([Fig. 73], d), platysma, and the skin. The inner surface is in relation caudad with the supraspinatus and with a mass of fat and a lymphatic gland which occupy the hollow of the shoulder. Craniad it is in relation with the cleidomastoid ([Fig. 73], d), the scalenus ([Fig. 73], f), the longus capitis ([Fig. 73], e), and the obliquus superior ([Fig. 71], e).
Action.—Pulls the scapula craniad.