PECTORALIS MINOR MUSCLE. 231 



Supposing both limbs fixed as in climbing, the trunk will be raised by 

 both muscles ; and the ribs can be elevated in laborious breathing. 



Dissection (fig. 70). The great pectoral muscle is to be cut across now 

 in the following manner : 



Only the clavicular part is to be first divided, so that the branches of 

 the nerve and artery to the muscle may be found. Reflect the cut part of 

 muscle, and press the limb against the edge of the table, for the purpose 

 of raising the clavicle and rendering tight the fascia attached to that 

 bone ; on carefully removing the fat, and a piece of fascia prolonged from 

 the upper border of the small pectoral muscle, the membranous costo- 

 coracoid sheath will be seen close to the clavicle, covering the axillary 

 vessels and nerves. 



At this stage the cephalic vein is to be defined as it crosses inwards to 

 the axillary vein. A branch of nerve (anterior thoracic), and the acro- 

 mial thoracic artery, which perforate the tube of membrane around the 

 vessels, are to be followed to the pectoral muscles. 



The remaining part of the pectoralis major may be cut about its centre, 

 and the pieces may be thrown inwards and outwards. Any fat coming 

 into view is to be removed ; and the insertion of the tendon of the pecto- 

 ralis is to be followed to the humerus. 



Insertion of the pectoralis. The tendon of the pectoralis consists of 

 two parts, anterior and posterior, at its attachment to the bone ; the ante- 

 rior receives the clavicular and upper sternal fibres, and joins the tendon 

 of the deltoid muscle ; and the posterior gives attachment to the lower 

 ascending fibres. The tendon is from two inches to two inches and a half 

 wide, and sends upwards one expansion over the bicipital groove to the 

 capsule of the shoulder-joint, and another to the fascia of the arm. 



Parts covered by the pectoralis. The great pectoral muscle covers the 

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

 rior boundary of the axilla. Between the pectoralis minor and the clavicle 

 it conceals the subclavius muscle, the sheath containing the axillary ves- 

 sels, 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 (fig. 70, B ) resembles the preceding muscle in 

 shape, and is extended like it from the thorax to the arm. Its origin is 

 connected by slips with the third, fourth, and fifth ribs, external to their 

 cartilages ; and between the ribs, with the aponeurosis covering the inter- 

 costal muscles. The fibres converge to their insertion in the anterior half 

 of the upper surface of the coracoid process of the scapula. 



This muscle is placed before the axillary space, and assists the pecto- 

 ralis major in forming the middle of the anterior boundary : in that po- 

 sition it conceals the axillary vessels and the accompanying nerves. The 

 upper border lies near the clavicle, but between it and that bone is an in- 

 terval of a somewhat triangular form. The lower border projects beyond 

 the pectoralis major, close to the chest ; and along it the long thoracic 

 artery lies. The tendon of insertion is united with the short head of the 

 biceps and the coraco-brachialis. 



Action. Acting with the serratus magnus it moves the scapula for- 

 wards and somewhat downwards. 



In laborious breathing it becomes an inspiratory muscle, as it takes its 

 fixed point at the scapula. . 



