20 



DISSECTION OF THE UPPER LIMB. 



Parts 



covered by 

 the muscle, 



Pectoral is 

 minor : 



origin ; 

 insertion ; 



relations ; 



Dissection 

 of axillary 

 sheath and 

 costo-co- 

 racoid 

 fascia. 



Costo-cora- 

 coid mem- 

 brane 



conceals 

 subclavius, 



and joins 

 sheath of 



vessels. 



Axillary 

 sheath 



strongest in 

 front. 



Clean the 



Parts covered by the pectoralis. The great pectoral muscle covers 

 the pectoralis minor, and forms alone, above and below that muscle, 

 the anterior boundary of the axilla. Between the pectoralis minor 

 and the clavicle it conceals the subclavius muscle, the sheath con- 

 taining the axillary vessels, and the branches perforating that sheath. 

 Below the pectoralis minor it lies on the side of the chest, on the 

 axillary vessels and nerves, and on the biceps and coraco-brachialis 

 muscles near the humerus. 



The PECTORALIS MINOR (figs. 6 and 7) is also triangular in 

 shape, and extends from the thorax to the shoulder. It arises 

 from the third, fourth, and fifth ribs, immediately external to their 

 cartilages, by tendinous slips which are blended with the aponeuroses 

 in the intercostal spaces. The fibres converge to their insertion into 

 the anterior half of the coracoid process of the scapula, at its upper 

 and inner part (fig. 10, p. 29). 



This muscle assists the pectoralis major in forming the anterior 

 wall of the axilla, and near its insertion it lies over the large vessels 

 and the accompanying nerves. The upper border is separated from 

 the clavicle by a triangular interval. The lower border projects 

 beyond the pectoralis major close to the chest; and along it the long 

 thoracic vessels lie. The tendon of insertion is united with the 

 coraco-brachialis and short head of the biceps. 



Action. It draws the scapula forwards and downwards ; and in 

 laborious breathing it becomes an inspiratory muscle, taking its fixed 

 point at the shoulder. 



Dissection. Supposing the clavicle raised by pressing back- 

 wards the arm, as before directed, the tube of fascia around the 

 axillary vessels will be demonstrated by making a transverse cut 

 below the costo-coracoid membrane so that the handle of the 

 scalpel can be passed beneath it. Then, by dividing the mem- 

 brane itself near the clavicle and raising the lower border of the 

 subclavius, this muscle will be seen to be encased by fascia, which is 

 attached to the bone both before and behind it. 



The costo-coracoid membrane or ligament is a firm band which 

 is attached on the inner side to the first rib, and on the outer- 

 side to the coracoid process of the scapula. Between these points it 

 is inserted into the under-surface of the clavicle, enclosing the sub- 

 clavius muscle (fig. 6 D). The fascia that encases the small pectoral 

 muscle is joined to the membrane above, and, in addition, the deep 

 stratum of the membrane, beneath the subclavius muscle, is blended 

 with the front of the axillary sheath. 



The sheath of the axillary vessels and nerves (E)* is a funnel- 

 shaped tube, prolonged from the fascia covering the scaleni muscles 

 in the lower part of the neck. It is strongest near the subclavius 

 muscle, where the costo-coracoid band joins it. The anterior part 

 of the sheath is perforated by the cephalic vein (e), the acromio- 

 thoracic artery (), and the anterior thoracic nerves ( l and 2 ). 



Dissection. After the costo-coracoid membrane has been ex- 



The letters and figures refer to fig 6. In fig. 7 the parts are named. 



