256 APPLIED ANATOMY. 



A distention of the joint will cause the deltoid to be more prominent. If the 

 affection is in an old person, as is liable to be the case in osteo-arthritis, there 

 is apt to be a communication with the subacromial bursa and this will become dis- 

 tended. If the liquid is purulent it has a tendency to work its way laterally under 

 the deltoid and break through at its anterior or posterior borders and show itself at 

 the folds of the axilla. 



In osteo-arthritis {arthritis deformans) the long tendon of the biceps as it passes 

 through the joint may be dissolved and the belly of the muscle then contracts and forms 

 a lump on the middle of the arm anteriorly. 



Pus frequently finds an exit along the bicipital groove and follows it downward 

 and shows itself just at the edge of the anterior axillary fold near the middle of the arm. 



If the pus passes out by way of the subscapular bursa it passes below the 

 subscapular tendon and into the axilla anteriorly. If it passes backward it may 

 emerge through the bursa beneath the infraspinatus muscle, and then either work its 

 way downward into the posterior portion of the axilla, or if it works upward may 

 travel either above or below the spine of the scapula and show itself on the dorsum. 



THE AXILLA. 



The axilla is a wedge-shaped space with its apex upward, formed between the 

 arm and chest at their junction. It serves as a passage-way for the arteries, veins, 

 nerves, and lymphatics passing between the trunk and the upper extremity. It is 

 frequently the site of growths and abscesses, requiring operations which necessitate a 

 knowledge especially of its blood-vessels and lymphatics. 



Extent. Its apex lies between the clavicle and scapula above and the first rib 

 beneath. Its base is formed by the skin and fascia stretched between the anterior and 

 posterior axillary folds. It is spoken of as having four walls: inner, outer, anterior, 

 and posterior. 



The inner wall is. formed by the first four ribs and interspaces and the corres- 

 ponding serrations of the serratus anterior (magnus) muscle. 



The outer wall is nothing more than the chink formed by the union of the two 

 axillary folds. Above is the lesser tuberosity of the humerus and subscapularis ten- 

 don, lower down are the coracobrachial and biceps muscles. 



The anterior wall is formed by the pectoralis major and minor muscles with the 

 fascia enveloping them. 



The posterior wall is formed by the subscapularis above and the teres major and 

 latissimus dorsi muscles below. 



Axillary Fascia. The name axillary fascia is given to the fascia which closes 

 the axillary space and forms its base. It is stretched across from the lower edge of 

 the pectoralis major in front to the lower edge of the teres major and latissimus dorsi 

 behind. On the inner wall it is continuous with the fascia covering the serratus 

 anterior (magnus) and side of the chest; when it reaches the vessels at the apex of 

 the axilla it is reflected around them to form the sheath. 



On the outer wall it passes from the pectoralis major in front, over the coraco- 

 brachialis muscle beneath, blends with the sheath of the vessels, and then passes to 

 the posterior wall, covering the subscapularis above and the teres major and latissi- 

 mus dorsi below. At the lower edge of this latter muscle, which is a little lower than 

 the pectoralis major, it passes across the axilla (Fig. 269). 



Anteriorly the fascia covers the pectoralis major muscle; at its lower edge it 

 splits to cover the pectoralis minor muscle and forms a sheath for it. As the axillary 

 fascia approaches the apex of the axilla where the superficial vessels enter, it becomes 

 cribriform in character, the fascia itself being wide-meshed and containing fat in the 

 interstices. If the handle of the scalpel is inserted in the apex of the axilla and 

 worked backward and forward two arches of fascia are readily formed, one convex 

 toward the chest, and called the " Achselbogen," and the other convex toward the 

 arm, called the " A rmbogen " (Langer, Oester. med. Woch., 1846, Nos. 15 and 16). 



The fascia on the superficial surface of the pectoralis minor is called the clavi- 

 pc dor al fascia. At the upper or inner border of the pectoralis minor it is continuous 



