358 PRACTICAL ANATOMY. 



greater tuberosity of the humerus. (Fig- 253.) Demonstrate the quadrangular 



and triangular spaces according to the outline given in the preceding pages. 

 (Fig. 251.) 



The Infraspinatus (Fig. 251). Now cut this muscle at its insertion into 

 the middle facet of the greater tuberosity ; turn the same backward, taking care 

 not to injure the capsule of the shoulder-joint and the vessels and nerves that 

 enter under the surface of the muscle. This muscle arises from the outer two- 

 thirds of the infraspinous fossa. (Fig. 252.) It is covered by a dense layer of 



Supra -apinatui 



Infra-spinatus 

 Teres minor V 



Teres major 



Long head of triceps 



Outer head of triceps 



Inner head of triceps 



FIG. 251. BACK VIEW OK THE SCAPULAR Mrsci KS AND TRICEPS. 



deep fascia. The muscle is triangular in shape, and derives its nerve-supply 

 from the infraspinous branch of the suprascapular nerve. 



The supraspinatus muscle (Fig. 251) arises from the outer two-thirds of 

 the fossa of the same name and also from the dense aponeurosis covering the 

 muscle. It is inserted into the upper facet of the greater tuberosity of the 

 humerus. It is covered (i) by a dense fascia of the same name ; (2) by the 

 trapezius muscle, which is inserted into the upper lip of the scapular spine. (Fig. 

 250.) Fxpose this supraspinatus muscle by cutting the insertion of the trapezius. 

 Then you may trace the supraspinatus under the acromion process to its inser- 





