160 THE MUSCLES. 
Action. —Extends the humerus after it has been flexed on 
the scapula. 
M. infraspinatus (Fig. 75, c).—This fills the infraspinatus 
fossa, its fibres converging to the insertion on the great tuber- 
osity of the humerus. 
Origin (Fig. 76, a).—By fleshy fibres from the whole infra- 
spinatus fossa, and by a raphe between it and the teres major 
Fic, 76.—LATERAL SURFACE OF THE SCAPULA, WITH THE AREAS OF ATTACH- 
MENT OF MUSCLES. 
«, M. infraspinatus; 4, M, supraspinatus; c¢, origin of M. biceps; ¢, M. acromio- 
deltoideus; ¢, M. teres minor: 7, M. levator scapulze ventralis; g, M. spinodeltoideus; 
h, M. acromiotrapezius; 7, M. rhomboideus; 7, M. teres major; 4-4, line of insertion 
of M. spinotrapezius. 
(Fig. 75, @), and sometimes by fibres from the teres minor 
(Fig. 80, c), triceps, spinodeltoideus (Fig. 75, ¢), spinotrapezius . 
(Fig. 68, 7), and subscapularis (Fig. 77, a). 
Insertion (Fig. 83, c).—By a flat tendon which passes over 
the capsule of the joint, into the ventral half of the infraspinatus 
fossa on the great tuberosity of the humerus. (The dorsal half 
of the fossa is covered by a synovial bursa.) 
Relations.—Outer surface with the spinotrapezius (Fig. 
68, 7), spinodeltoid (Fig. 68, 7), acromiodeltoid (Fig. 68, g), 
teres major (Fig. 75, @), and levator scapule ventralis (Fig. 
