i6o 



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. y6, a). — By fleshy fibres from the whole infra- 

 spinatus fossa, and by a raphe between it and the teres major 



Fig. 76. — Lateral Surface of the Scapula, with the Areas of Attach- 

 ment OK Muscles. 

 a, M. infraspinatus; b, M. supraspinatus; c, origin of M. biceps; d, M. acromio- 

 deltoideus; e, ^I. teres minor; /, M. levator scapulit ventralis; g, M. spinodeltoideus; 

 h, M. acroniiotrapezius; ?', M. riiomboideus; y, M. teres major; k-l, lineof insertion 

 of M. spinotrapezius. 



(Fig. 75, d), and sometimes by fibres from the teres minor 

 (Fig. 80, c), triceps, spinodeltoideus (Fig. 75, c), spinotrapezius 

 (Fig. 68, y), and subscapularis (Fig. yj, 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, y), spinodeltoid (Fig. 68, /), acromiodeltoid (Fig. 68, g), 

 teres major (Fig. 75, d), and levator scapulae ventralis (Fig. 



