710 MUSCLES OP THE SHOULDER. 



Deltoid A, delta, *t8oj, likeness, (Figs. 150,167.) Dissec- 

 tion. Make the first incision along the posterior third of 

 the clavicle, the acromial margin, and spine of the scapula; 

 the second from the acromion process, along the middle of 

 the humerus, and commence the dissection from this last 

 incision, turning off the integuments internally and exter- 

 nally with the cellular structure, when this muscle will he 

 exposed. It arises from the external third of the clavicle, 

 fleshy; from the outer margin of the acromion process, ten- 

 dinous and fleshy ; and from the whole of the inferior edge 

 of the spine of the scapula. It is inserted on the outer side 

 of the humerus,near its centre, in a triangular rough surface. 



This muscle is triangular in shape, thick and strong, cov- 

 ers the shoulder-joint, and gives it its rotundity. The fibres 

 converge the anterior descending obliquely backward, the 

 posterior forward, and the middle directly downward, the 

 three presenting so many separate parts or muscles. 



Function. To raise the arm. and, according to the direc- 

 tion of the fibres, to draw it either forward or backward. 

 Beneath the superior portion of this muscle, extending 

 under the acromion process, is seen a large bursa. 



Supra-spinatus supra, above ; spina, the spine (Fig. 

 150.) By turning down the deltoid this muscle is seen ; it 

 arises fleshy from the whole of the supra-spinal fossa, also 

 from a strong fascia covering it ; it then passes under the 

 acromion process, ending in a strong tendon, which is 

 firmly attached to the capsular ligament, and is inserted 

 into the inner face of the greater tuberosity of the humerus. 



Function. To raise the arm and turn it outward ; also 

 to strengthen the capsular ligament, and to draw it from 

 "between the humerus and glenoid cavity, in the elevation 

 of the arm. 



Infra spinatus infra, beneath ; spina, spine (Fig. 150,) 

 arises from the whole of the dorsum of the scapula below 

 its spine, from the margins of the bone, and from the 

 aponeurosis covering it, forming a flat, triangular muscle. 

 Its fibres converge, the superior going horizontally, the 

 inferior ascending obliquely forward, to a strong central 



