PECTORALIS MAJOR. 19 



forms the anterior fold of the hollow. Covering it are the integu- 

 ments, with the mamma and the thin deep fascia, as well as the 

 platysma close to the clavicle. The upper border is adjacent to the 

 deltoid muscle, the cephalic vein, and a small artery lying between 

 the two. Between the clavicular and sternal origins is a narrow 

 interval, which corresponds to a depression on the surface. The 

 parts beneath the pectoralis major will be seen subsequently. 



Action. If the humerus is hanging, the muscle will move Use: flexes, 

 forwards the limb until the elbow reaches the front of the trunk, rotates iri > 

 and will rotate it inwards. 



When the limb is raised, the pectoralis depresses and adducts it and add nets 

 (draws it to the side of the body) ; and acting with other muscles arm> 

 inserted into the humerus, it may dislocate the head of that bone 

 when the lower end is raised and fixed, as in a fall on the elbow. 



Supposing both limbs fixed, as in climbing, the trunk will be raises ribs, 

 raised by both muscles ; and the lower fibres can elevate the ribs 

 in laborious breathing. 



Dissection (figs. 6 and 7). The great pectoral muscle is to be cut Dissection, 

 across now in the following manner : 



Divide the clavicular part of the muscle and find the subjacent Cutciavi- 

 branches of nerve and artery. In reflecting the cut piece of the of Uie Pai 

 muscle, press the limb against the edge of the table, for the P ectoral - 

 purpose of raising the clavicle and rendering tight the fascia 

 attached to that bone. Carefully remove 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. 



The cephalic vein is to be defined as it crosses inwards to the Trace 

 axillary vein. A branch of a nerve (the external anterior thoracic), 

 and the acromio-thoracic vessels, perforate the fascia over the axillary 

 trunks, and are to be followed to the clavicular part of the pectoral 

 muscle. A second branch of the external anterior thoracic nerve, 

 with accompanying arteries, will be found passing downwards over 

 the upper border of the pectoralis minor into the sternal part of the 

 major muscle. These nerves and arteries should now be cleaned. 



The remaining part of the pectoralis major may then be cut about Divide the 

 its centre, and the pieces thrown inwards and outwards. Any fat n iuscie. the 

 coming into view is to be removed ; and the tendon of the pectoralis 

 is to be followed to the humerus. In raising the pectoralis major 

 note will be taken of a small nerve (internal anterior thoracic), 

 which usually pierces the minor muscle to enter the lower part of 

 the major. 



Insertion of the pectoralis major. The tendon of the pectoralis Tendon of 

 consists of two layers, anterior and posterior, at its attachment to pec1 

 the bone ; the anterior receives the clavicular and upper sternal 

 fibres ; and the posterior gives attachment to the lower ascending 

 thoracic 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 downwards 

 to the fascia of the arm (see humerus, fig. 17, p. 44). 



c 2 



