MUSCLES OF THE ANTERIOR LIMBS. 249 



MUSCLES OF THE SHOULDER. 



These muscles are grouped around the scapula, and all act upon the arm, 

 which they extend, flex, abduct, adduct, etc. They form two regions : an 

 external or suprascapular, and an internal or subscapular. 



A. External Scapular Region. 



This comprises four muscles : the long abductor of the arm, the short 

 abductor, the super- (or supra-) spinatus, and sub- (or infra-) spinatus. These 

 muscles are applied to the external surface of the scapula, and are covered 

 by an aponeurotic lamella. 



Preparation of the external scapular region. Separate the limb from the trunk; 

 remove the trapezius and mastoido-humeralis, to expose the external surface of the 

 aponeurosis; take away, also, the small pectoral muscle, after studying its mode of 

 insertion into this fascia. 



This being accomplished, next remove the latter muscle to show the supraspinatus, 

 the subspinatus, and long abductor muscle of the arm ; leaving only the strip which 

 attaches the anterior portion of the latter to the tuberosity of the scapular spine. 



To study the short abductor muscle, it is only necessary to cut the long abductor and 

 superspinatus across, and to throw back the sections : an operation requiring some care, 

 because of the intimate adherence of the short abductor to the infraspinatus. 



1. External Scapular Aponeurosis. 



This aponeurosis, to which the sterno-prescapularis and long adductor of 

 the arm act as tensors, gives origin, by its internal face, to several septa 

 which penetrate between the scapular muscles, and form around them more 

 or less complete contentive sheaths. Its external face is separated from the 

 skin by the panniculus carnosus, trapezius, mastoido-humeralis, and the 

 aponeurotic fascia which unites the last two muscles. It is continuous, in 

 front, with the thin fibrous expansion extended over the internal scapular 

 muscles ; behind and downwards, it is prolonged over the muscles of the arm 

 and insensibly degenerates into conjunctival tissue ; above, it is attached 

 to the fibre-cartilaginous prolongation of the scapula. 



2. Long Abductor of the Arm, or Scapular Portion of the Deltoid. 

 (Fig. 119, 1, 1.) 



Synonyms. Scapulo-humeralis magnus Girard. (Teres major Percivatt. Great 

 scapulo-trochiterius Leyh.) 



Situation Composition Form Direction. This muscle is situated 

 beneath the scapular aponeurosis, behind the subspinatus, and is composed 

 of two portions placed one above the other, separated by a superficial inter- 

 space. The posterior portion, the most considerable, is elongated from 

 above to below, bulging in its middle, narrow at its extremities, plane on its 

 external, and convex on its internal surface. It accompanies the posterior 

 border of the subspinatus, and is lodged in a depression in the thick 

 extensor muscle of the fore-arm. 



The anterior portion, much shorter than the preceding, extends over the 

 subspinatus and short abductor, by slightly crossing the direction of these 

 two muscles. Thick inferiorly, this portion diminishes considerably towards 

 its superior extremity. 



