302 



THE MUSCLES 



by the suprascapular liranch wliieli enters the muscle upon its deep aspect near its 

 upper border. 



Action. — It assists the deltoid in al)duetin<r the arm; it also strengthens the 

 shoulder-joint l)y resisting the tendency to u})\vard disj)lacement of the head of 

 the luunerus, and by drawing the head of the humerus tirmly towards the centre of 

 the glenoid cavity. 



Fig. 268. — Back View of the Scapulae Muscles and Triceps. 



Supra-spinatus 



Infra-spinatus ''^£ 

 Teres minor 



Teres major 



Long head of triceps 



Outer head of triceps 



Inner head of triceps 



Relations. — Su]ierficially, the trapezius, deltoid, and coraco-acromial ligament; 

 deeply, the oino-hyoid muscle and capsular ligament, the suprascapular vessels and 

 nerve. 



3. INFRA-SPINATUS 



Tlie infra-spinatus — named from its position below the spine of the sca])ula — 

 is a thick, fan-shaped slieet. 



Origin.— (1) The inner two-thirds of tlie infraspinous fossa; (2) the under 

 surface of the spine of the scai)ula; (3) the infraspinous fascia, and a thick inter- 

 muscular septum which separates it from the teres minor and major muscles. 



Insertion. — (1) The middle facet on the greater tuberosity of the humerus; 

 and (2) the ea])sule of the shonlder-joint. 



