242 DISSECTION OF THE UPPER LIMB. 



dorsi, and the long head of the triceps : along this border is the subscapular 

 artery, which gives backwards its dorsal branch. 



Action. It rotates in the hanging limb ; and when the humerus is raised 

 it depresses the bone. 



If the humerus is fixed the subscapularis supports the shoulder joint with 

 the other scapular muscles. 



Dissection. The subscapular muscle is to be separated from the scapula, 

 but a thin layer of fibres, in which the vessels lie, is to be left on the bone : 

 as it is raised its tendinous processes of origin, the connection between its 

 tendon and the capsule of the shoulder joint, and the bursa, are to be ob- 

 served. A small arterial anastomosis on the ventral surface of the bone 

 is to be dissected out of the fleshy fibres. 



The infrascapular artery ramifies on the ventral surface of the scapula, 

 and is an offset of the dorsal branch of the scapular vessel (p. 335): en- 

 tering beneath the subscapularis muscle, it forms an anastomosis with small 

 twigs of the supra and posterior scapular branches. 



Position. The examination of the muscles on the opposite surface of the 

 scapula may be next undertaken. For this purpose the scapula is to be 

 turned over ; and a block, which is deep enough to make the shoulder 

 prominent, is to be placed between that bone and the arm. 



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

 shoulder, by beginning at the anterior border of the deltoid muscle. After 

 its removal some small cutaneous nerves are to be found in the fat: the 

 upper of these extend over the acromion ; and another comes to the sur- 

 lace about half way down the posterior border of the deltoid muscle. 



Superficial nerves. Branches of nerves, super-acromial, descend to the 

 surface of the shoulder from the cervical plexus (p. 66). A cutaneous 

 branch of the circumflex nerve (fig. 74, 2 ) 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 fleshy del- 

 toid, its fibres being made tense at the same time. Beginning at the 

 anterior edge of the muscle, the dissector is to carry the knife upwards and 

 downwards along the fibres, in order that its coarse muscular fasciculi may 

 b'3 more easily cleaned. As the posterior edge is approached, the cuta- 

 neous nerve and artery 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 is triangular in form (fig. 74, p ), with the base at 

 the scapula and clavicle, and the apex at the humerus. It arises from 

 nearly all the lower edge of the spine of the scapula, from the anterior 

 edge of the acromion, and from the outer half or third of the clavicle. Its 

 fibres converge to a tendon, which is inserted into a triangular impression, 

 two or three inches long and about one inch wide at the base, above the 

 middle of the outer surface of the humerus. 



The anterior border is contiguous to the pectoralis major muscle and the 

 cephalic vein ; and the posterior rests on the infraspinatus and triceps 

 muscles. The origin of the muscle corresponds with the attachment of 

 the trapezius to the bones of the shoulder; the insertion is united with 

 the tendon of the pectoralis major, and a i'asciculus of the brachialis 

 anticus is attached on each side of it. 



Action The whole muscle raises the humerus, and abducts it from 



