THE PECTOEAL MUSCLES. 193 



n. BETWEEN THE TRTJNK ANI> THE UPPER LIMB ANTERIORLY. 



Fasci.i<:. — The superficial fascia of the pectoral region encloses the 

 mammary gland, covering it both in front and behind, and sending 

 strong septa in between its lobes. Processes likewise extend forwards 

 from the fascial investment of the gland, between the masses of fat, to 

 the skin and nipple, thus affording support to the gland. 



The deep fascia of the pectoral region is continuous with that of 

 the neck both before and behind the clavicle, and with the similar 

 structure spreading over the shoulder and thorax. As belonging to the 

 deep fascia there may be specially noticed the costo-coracoid membrane, 

 which is a distinct layer of firm fascia, attached superiorly to the 

 clavicle and giving a firm covering to the subclavius muscle. Its 

 strong lower margin, distinguished sometimes as the costo-coracoii/ 

 ligament, extends fi"om the coracoid process to the first rib at the origin 

 of the subclavius muscle. The deep fascia, continued from this struc- 

 ture inferiorly, is narrowed like a funnel, and becomes thinner as it 

 descends upon the surface of the axillary vessels, forming the anterior 

 part of the sheath of those vessels, while the posterior part is formed 

 by a deep process of the cervical fascia. 



The axillary fascia is a strong membrane stretched across the 

 axilla, and so disposed as to maintain the skin in position over that 

 hollow. Beneath the pcctoralis major muscle is a layer of fascia attached 

 to the chest in front of the costo-coracoid membrane : it divides into 

 two layers to enclose the pectoralis minor, and, these reuniting, it con- 

 tinues to pass outwards as a strong membrane between the pectoralis 

 minor and short head of the biceps muscle ; lower down it is joined 

 by the fascia covering the pectoralis major, which is folded round the 

 margin of that muscle, and, thus strengthened, it slopes outwards 

 and backwards to the inferior border of the scapula, where it is joined 

 by the sheaths of the latissimus dorsi and teres major muscles. In 

 the deepest part of the axilla the fascia is perforated by numerous 

 blood-vessels and Ivmphatics. At the outer side occupied by the 

 large vessels and nerves of the limb, it is continuous with the sheath 

 of the vessels and with the aponeurosis of the arm. The density 

 of this fascia offers a considerable obstacle to the progress of axillary 

 abscesses to the surface. 



Muscles. — The pectoralis major muscle arises from the anterior 

 and lower surface of the sternal half of the clavicle ; from the anterior 

 surface of the sternum ; from the cartilages of the second to the sixth 

 ribs, and also the bony part of the sixth rib ; and from the aponeurosis 

 of the external oblique muscle of the abdomen. Its fibres form a thick 

 mass, and converge to be inserted by a tendon of considerable breadth into 

 the outer bicipital ridge of the humerus. At the axillary border the 

 muscular fasciculi, especially those of the pectoral part, are folded back- 

 wards, so that the lower fibres successively disappear from view, and 

 the insertion into the humerus takes place by a broad flat tendon which 

 is doubled upon itself in two close parallel lines, open above and con- 

 nected below. The clavicular fasciculi are for the most part inserted on 

 the outer surface of the anterior fold of the tendon, but they are also 

 continued by independent tendon directly to the humerus. The posterior 

 fold of the pectoral tendon is usually considerably broader than the 

 anterior, and thus its line of attachment rises higher on the humerus. 



VOL. I. 



