Practicum II. The Shoulder Muscles. 11 



8. Note the Remnant of the Pectoral Mass mostly on the cephalic and 

 "outer" aspect of the brachium ; on the caudal and "inner" side is an- 

 other mass consisting of the latissimus and the TERES, a shorter muscle 

 extending from the caudal margin of the scapula to the humerus. If the 

 latissimus and teres be drawn entad from the brachium there will appear, 

 passing from them to beyond the elbow a wide and strong FASCIA, 

 almost a tendon ; between it and the brachium is connective tissue which 

 may be cut or torn. 



a. On the ental side of the shoulder, in a ragged mass between the 

 pectoral and latissimus are a NERVE, a BLOOD-VESSEL, and connective tis- 

 sue. Into the space loosely filled by them crowd the thumb or a scalpel 

 handle. The space will be found bounded by a MUSCULO-FIBROUS ARCH. 



9. Cut the Arch at its Highest Point, between the pectoral and latissi- 

 mus masses. Turn these in opposite directions. Note that they covered 

 a fusiform, slender muscle, the BICEPS, PI. V, and that along its inner 

 side, near the humerus, passes a NERVE, the musculo-cutaneous ; see 18. 



10. On the Ectal Surface of the Scapula is a thin sheet of muscle 

 and fascia attached to the bony ridge (spine) which projects from it. Cut 

 along the line of this attachment and remove. 



ii. Removal of Other Muscles. Keeping the biceps constantly in 

 mind, the muscles about the shoulder may be removed as follows : 



a. Transect the mass covering the ental aspect of the scapula at about 

 the middle of its length, i. e., at the word muscle in PL V ; after 

 dividing the muscle with the scalpel use the arthrotome and cut down to 

 the bone. Peel the proximal (dorsal) part of the muscle off, noting that : 



1. The fibers diverge toward the vertebral border. 



2. They arise not by ordinary tendons but directly from the peri- 

 osteum. The periosteum may be lifted on the point of the scalpel. 



b. On the lateral aspect is a bony ridge, the "spine" of the scapula, 

 shown but not named on PL I. Avoiding that, the muscles at either side 

 of it are to be transected at about one-third the way from the dorsal bor- 

 der. Note that they arise from the "spine," as well as from the general 

 surface of the scapula. 



12. Relation of the Muscles to the Shoulder Joint. Cut between 

 the distal portions of the three muscles along the margins of the scapula 

 and peel them off to the shoulder. Their attachments cover the shoulder 

 joint so as to lessen the liability to dislocation of the head of the humerus 

 from the shallow glenoid cavity. Note that pulling upon them moves the 

 arm in corresponding directions : also that various combinations of the 

 three muscles enable the arm to be rotated in intermediate directions. 



13. The Capsule of the Shoulder. Transect all the muscles at the 

 head of the humerus so as to expose in some degree the fibrous capsule of 

 the joint, comparable with what was seen at the hip ; Pract. I, 5, b. 



14. The Triceps. The "elbow" side (dorsum) of the brachium pre- 

 sents a thick mass of mucles which may here be designated under the 

 general name TRICEPS. 



15. The Brachial Plexus. On the ental side of the arm are several 

 white, thick, firm NERVES. These are part of the Brachial Plexus, Pr. I, 

 17, *:, PL IV, and were cut in removing the arm. 



16. The Ulnar Nerve. In the interval between the biceps and the 

 triceps, on the ulnar ("inner") side, search with the tracer for a large 



