230 FASCIAE OF THE UPPER LIMB. 



which conceals that muscle from view. Superiorly it is attached to the 

 clavicle ; inferiorly it 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 across that hollow. Beneath 

 the pectoralis 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 continues to pass outwards, forming 

 a strong membrane in the angle between the pectoralis minor and short head 

 of the biceps muscle; lower down it is joined by the superficial investment 

 of 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. The deepest hollow of the axillary fascia is formed 

 where the layer from the surface of the pectoralis major joins that from the 

 pectoralis minor ; and in that part especially it is perforated by numerous 

 lymphatics. At the angle occupied by the large vessels and nerves of the 

 limb, it is continuous with the sheath of the vessels and with the aponeu- 

 rosis of the arm. The density of this fascia offers a considerable obstacle to 

 the progress outwards of axillary abscesses. 



The aponeurosis of the upper limb is a strong sheath which binds together 

 all the muscles of the arm and forearm. A strong and somewhat isolated 

 portion, bound down to the vertebral and axillary margins and to the lower 

 border of the spine of the scapula, covers the infraspinatus and teres minor 

 muscles as far as they are left uncovered by the deltoid muscle. On reaching 

 the posterior border of the deltoid muscle, this aponeurosis divides into two 

 layers, of which the deeper is continued beneath the deltoid to the shoulder- 

 joint, and the more superficial forms a thin aponeurotic covering of that 

 muscle, becoming more and more slender as it passes forwards. 



The aponeurosis of the arm is composed chiefly of transverse fibres, held 

 together by others having an oblique or longitudinal direction ; it is thin over 

 the biceps muscle, stronger where it covers the triceps, and particularly 

 dense as it approaches the outer and inner condyloid eminences of the 

 humerus. It is pierced on the inner side of the limb by the basilic vein, 

 at some distance below the axilla. It is attached to the shaft and condyloid 

 eminences of the humerus by the two processes next to be described. 



The external and internal intermuscular septa are two fibrous partitions 

 which bind the aponeurosis of the arm to the humerus, and with which the 

 neighbouring muscles of the arm are intimately connected. The external inter- 

 muscular septum extends upwards from the outer condyloid eminence along 

 the outer lateral ridge to the insertion of the deltoid, from which it receives 

 tendinous fibres. It is pierced from behind forwards by the musculo-spiral 

 nerve and superior profunda artery. The internal septum, much stronger, 

 extends along the ridge from the inner condyloid eminence to the insertion 

 of the coraco-brachialis muscle. It is traversed from before backwards by the 

 ulnar nerve and by the inferior profunda and anastomotic arteries. 



At the bend of the elbow the aponeurosis is closely connected with the 

 periosteum covering the condyloid eminences of the humerus and the ole- 

 cranon process of the ulna ; arid it is strengthened by tendinous fibres sent 

 from the triceps and biceps muscles. 



The apcneurosis of the forearm, like that of the arm, is composed principally 



