50 THE UPPER EXTREMITY 



and () of several fine filaments which pierce the substance 

 of the deltoid muscle, and appear at irregular intervals on 

 its surface. The latter are difficult to secure, but the main 

 branch can be easily found by carefully dividing the superficial 

 fascia along the posterior border of the deltoid. On everting 

 this border very little dissection is required to expose the 

 nerve hooking round it about two and a half inches above 

 the insertion of the deltoid (Fig. 22). It breaks up into 

 branches which supply the skin over the lower portion of the 

 deltoid region. 



Deep Fascia. A firm but thin fascia covers the subscapu- 

 laris muscle. Into this some of the fibres of the serratus 

 anterior are usually inserted at the vertebral border of the 

 scapula. The strongest and most conspicuous fascia in 

 this region is that which covers the exposed part of the 

 infraspinatus muscle on the dorsal aspect of the scapula. 

 It is firmly attached to the limits of the fossa in which that 

 muscle lies, and presents other very apparent connections. 

 Thus a strong septum, proceeding from its deep surface, will 

 be noticed to dip in between the infraspinatus and teres 

 minor muscles, and then, as it proceeds forwards, it gives a thin 

 covering to the teres minor, teres major, and the deltoid. In- 

 deed, it may be said to split into two lamellae a superficial 

 and a deep, which as they pass forwards enclose between 

 them the deltoid muscle. 



Dissection. Depress the scapula and retain it in this position by means 

 of hooks. The fibres of the deltoid are thus rendered tense, and the coarse 

 fasciculi of the muscle may be cleaned. 



M. Deltoideus. The deltoid muscle, as its name implies, 

 is triangular in form. It is composed of coarse fasciculi, and 

 covers the shoulder-joint. It arises from the anterior border 

 of the lateral third or half of the clavicle (Fig. 18, p. 41), 

 from the lateral border of the acromion and from the 

 lower border of the spine of the scapula (Fig. 24, p. 55). 

 Its origin closely corresponds with the insertion of the 

 trapezius. The fasciculi of which the muscle is formed 

 converge rapidly as they are traced distally, and finally they 

 are attached, by a pointed tendinous insertion, to the deltoid 

 eminence on the middle of the lateral surface of the body 

 of the humerus (Fig. 33, p. 79). Its nerves of supply come 

 from the axillary (circumflex) nerve. 



