464 



77/7:7 MUSCLES AND FASCIAE 



Actions. The Deltoid raises the arm directly from the side, so as to bring it to a right angle 

 with the trunk, but this act cannot be performed without the aid of the Serratus magnus, which 

 muscle steadies the lower angle of the scapula. Its anterior fibres, assisted by the Pectoralis 

 major, draw the arm forward ; and its posterior fibres, aided by the Teres major and Latissimus 

 dorsi, draw it backward. 



Applied Anatomy. The Deltoid is very liable to atrophy, and when in this condition dislo- 

 cation of the shoulder-joint is simulated, as there is flattening of the shoulder and apparent 

 prominence of the acromion process; upon examination, however, it will be found that the 

 relative position of the greater tuberosity of the humerus to the acromion and coracoid process is 

 unchanged. Atrophy of the Deltoid may be due to disuse or loss of trophic influence, either 

 from injury to the circumflex nerve (as in "crutch-palsy") or from spinal cord lesions, as in 

 infantile paralysis. In the operation performed for the obliteration of the subdeltoid bursa, the 

 incision through the Deltoid should be as far anterior as possible, in order to avoid severing the 

 nerves which enter the muscle from behind. 



4. The Anterior Scapular Region. 



Subscapularis. 



Dissection. Divide the Deltoid across, near its upper part, by an incision carried along the 

 margin of the clavicle, the acromion process and spine of the scapula, and reflect it downward, 

 when the structures under cover of it will be seen. 



8UPRASPINATUS 

 SUBSCAPULARIS 



PECTORALIS 

 MAJOR 



EXT. CAR 

 RAD. LONGI 



COMMON TENDON 

 FOR EXTENSORS 



-PRONATOR TERES 



.COMMON TENDON 



FOR FLEXORS 



LEX. SUBL. DIG. 

 ACH. ANT 

 3NATOR TERES 



FIG. 350. Diagram showing attachment of muscles of the shoulder and arm. Anterior aspect. 



Origins, red; insertions, blue. 



The subscapular fascia (fascia Subscapularis) is a thin membrane attached to 

 the entire circumference of the subscapular fossa, and affording attachment by 

 its inner surface to some of the fibres of the Subscapularis muscle. 



