414 MUSCLES. 



SECT. II. OF THE MUSCLES OF THE SHOULDER. 



The Ddtoides, 



Is a muscle which is extended over the top of the shoulder 

 joint, and forms there the subcutaneous cushion of flesh which 

 protects and gives rotundity to the articulation. It arises from 

 the inferior edge of the whole spine of the scapula, from the 

 circumference of the acromion process, and from the exterior 

 third of the clavicle. Its origin, for the most part, is tendinous 

 and fleshy mixed; but at its posterior part it is entirely tendi- 

 nous. 



It is inserted, by a tendinous point, into the triangular rough 

 surface on the outer side of the os humeri near its middle. Its 

 general configuration is triangular, and when spread out, its 

 upper margin is much more extensive than one would suppose, 

 as it is opposed to the entire insertion, of the trapezius. Its 

 fibres do not converge regularly to its insertion like the radii 

 of a circle, but the whole muscle is divided into several parts; 

 the interposition of inter-muscular tendons into which, affecting 

 the course of the fibres, makes several portions of the deltoid 

 look penniform, and others like smaller deltoids introduced into 

 the larger. 



The deltoid covers the insertion of the pectoralis major, latis- 

 simus dorsi, and teres major, besides that of the other muscles 

 of the shoulder. It also conceals the origin of the biceps flexor 

 cubiti and of the coraco-brachialis. Its insertion is between the 

 triceps extensor and the biceps flexor, and above the origin of 

 the brachialis interims.* 



It raises the os humeri. 



Between the superior edge of the deltoid, the acromion pro- 

 cess, and the subjacent tendons on the top of the articulation, 

 there is a large Bursa Mucosa, which is sometimes partitioned 

 off into two. 



* Varieties. Sometimes a fasciculus arises, between the infra-spinatus, find 

 the teres major, or from the inferior costa of the scapula, and joins itself to the 

 deltoids. 



