THE DELTOID. 31 



is contiguous to the teres major, the latissimus dorsi, and the long 

 head of the triceps. The subscapular artery runs along this border, 

 and its dorsal branch, as well as the posterior circumflex artery and 

 tin' circumflex nerve, turn backwards below it. 



A <-t ion. It rotates the humerus inwards, and when it is raised use. 

 it depresses that bone. 



Dissection. The subacapularis is to be separated from the Dissection 

 .scapula, except that a thin layer of fibres, in which the vessels lie, of the 

 is to be left on the bone. As the muscle is raised, its tendinous 

 processes of origin, the connection between its tendon and the cap- 

 sule of the shoulder-joint, and the bursa are to be observed. A 

 small arterial anastomosis on the ventral surface of the scapula is 

 to be dissected out of the fleshy fibres. 



The INFRASCAPULAR ARTERY is an offset of the dorsal branch of small infra- 

 the subscapular vessel (p. 24), and ramifies on the ventral surface 

 of the scapula. Passing beneath the subscapular muscle, it forms 

 an anastomosis with small twigs of the suprascapular and posterior 

 scapular arteries. 



Position. The examination of the muscles 011 the dorsal surface Position of 

 of the scapula may be next undertaken. For this purpose the im ' 

 limb is to be turned over ; and a block, which is deep enough to 

 make the shoulder prominent, is to be placed between the scapula 

 and the arm. 



Dissection. The skin is to be removed from the prominence of Dissection 

 the shoulder, down to the middle of the outer side of the arm. shoulder. 

 After its removal some small cutaneous nerves are to be found in 

 the fat : the upper of these descend over the acromion ; and 

 a larger branch comes to the surface about half-way down the 

 posterior border of the deltoid muscle. 



SUPERFICIAL XERVES. Branches of nerves, supraacromial, descend Cutaneous 

 to the surface of the shoulder from the cervical plexus. A cutaneous ne 

 branch of the circumflex nerve (tigs. 13 and 23) turns forwards with 

 a small companion artery from beneath the posterior border of the 

 deltoid, and supplies the integuments covering the lower two-thirds 

 of the muscle. 



Dissection. The fat and fascia are now to be taken from the Dissection 

 fleshy deltoid, its fibres being made tense for the purpose. Be- muscle? 1 

 ginning at the anterior edge of the muscle, the dissector is to carry 

 the knife upwards and downwards, following the direction of the 

 coarse muscular fasciculi. As the posterior edge is approached, 

 the cutaneous nerve and vessels escaping from beneath it are to be 

 dissected out. 



At the same time the fascia may be removed from the back of 

 the scapula, so as to denude the muscles there. 



The DELTOID MUSCLE (fig. 13 F,) is triangular in form, with Deltoid 

 the base at the scapula and clavicle, and the apex at the humerus. m 

 It arises from the whole length of the lower border of the spine 

 of the scapula, the origin being aponeurotic towards the vertebral 

 border of the bone and blending with the dense fascia over the origin 

 infraspinatus muscle, from the outer edge of the acromion (fig. 12), 



