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-spinatua 



Infra-spinatua 

 Teres minor 



Teres major 



Long head of triceps 



Outer bead of triceps 



Inner bead of triceps 



FIG. 251. BACK VIEW OK THE SCAPULAR MUSCLES AND IK 



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

 from the infraspinous branch of the suprascapular nerve. 



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

 the fossa of the >ame name and also from the dense aponcurosis covering the 

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

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

 trape/.ius muscle, which is inserted into the upper lip of the scapular spine. (Fig. 

 250.) Kxpose this supraspinatus muscle by cutting the insertion of the trape/ius. 

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



