AXILLA. 



361 



It is plain from this view of the parts that a 

 wound in the axilla, near the clavicle, might 

 penetrate both the artery and vein, and be fol- 

 lowed by aneurismal varix, but that no such 

 consequence could follow a puncture of these 

 vessels lower down. We see too that there 

 would be much difficulty in compressing the 

 axillary artery through the anterior wall of the 

 axilla, (formed as it is of the two pectorals,) ex- 

 cept in the triangular interval between the 

 great pectoral and deltoid muscles close to the 

 clavicle, and that the subclavius muscle and 

 the ligamentum bicorne would bear off pres- 

 sure even there to a great extent. In this place 

 the vein and artery lie closer to each other than 

 they do above the clavicle, a circumstance to 

 be remembered in attempting to command the 

 circulation of the limb. Collections of pus are 

 often met with in the cellular tissue under the 

 great pectoral muscle. In children they will 

 frequently be found to have been occasioned 

 by laceration which the tissue has suffered in 

 the act of raising them up by the arm. These 

 abscesses elevate the muscle considerably, and 

 do not always point in the lower part of the 

 axilla as might be expected. They approach 

 the surface directly in front in some cases. But 

 if an early opening were not made, it is pro- 

 bable they would oftener extend themselves all 

 through the axilla. 



The nerves in the axilla are large, numerous, 

 and complicated. The principal ones are in a 

 bundle, at first behind the axillary artery and 

 then surrounding it. They arise in the cervical 

 region, interlace in a remarkable way to form 

 the axillary or brachial plexus, give off some 

 branches in the neck, and on reaching the axilla 

 separate to supply the arm, forearm, and hand. 

 (For a particular description of this plexus 

 we refer to the article CERVICAL NERVES.) 

 The nerves we meet with in the axilla, besides 

 the costo-humeral, are, three thoracic branches, 

 three subscapular, and six others of much 

 greater size, viz. the external cutaneous, median, 

 internal cutaneous, ulnar, musculo-spiral, and 

 circumflex. 



The thoracic branches are most commonly 

 three in number ; the anterior, arising from the 

 seventh cervical, runs in front of the great ves- 

 sels and is lost in the pectoralis major and 

 pectoralis minor muscles ; the middle, very 

 small, passes under the vessels and is lost in 

 the lesser pectoral ; the posterior, the largest, 

 is the respiratory, and has been already de- 

 scribed. 



The subscapular branches are also three in 

 number generally ; they come from different 

 points at the upper and back part of the plexus: 

 the smallest quickly enters the subscapular 

 muscle : the other two sometimes arise by a 

 common trunk, or one of them comes from the 

 circumflex, both run along with the sub- 

 scapular artery, the larger pierces the teres 

 major and is lost in the latissimus dorsi, the 

 smaller is distributed to the subscapularis, teres 

 major and teres minor. 



The external cutaneous, ovperforans Casserii, 

 comes from the external part of the plexus, 



chiefly from the fifth and sixth cervical branches, 

 and leaves the axilla by running downwards and 

 outwards. It is superficial and external to the 

 axillary artery. 



The median arises from the front of the 

 plexus by two roots, one of which is placed on 

 each side of the artery ; they soon unite, the 

 nerve then lies on the artery, and inclining a 

 little outwards escapes from the axilla, being 

 destined principally for the hand. 



The internal cutaneous issues from the inter- 

 nal and inferior part of the plexus, lies very su- 

 perficially along the inner side of the artery, 

 and quits the axilla where the basilic vein is 



entering. 



The ulnar, arising from the internal and pos- 

 terior part of the plexus, inclines backwards, 

 separating itself slowly from the inner side of 

 the artery. 



The musculo-spiral arises still farther back, 

 and is concealed from view by the other 

 nerves. 



The circumflex nerve arises above and be- 

 hind all the others, and completely concealed 

 by them ; it descends before the subscapular 

 muscle for a little, then turns backwards and 

 outwards, close to the capsular ligament of the 

 shoulder-joint, and in company with the pos- 

 terior circumflex artery ; then it appears on the 

 outside of the neck of the humerus, between 

 the long head of the triceps, the bone, and the 

 teres major and minor muscles, and soon enters 

 the deltoid in two branches. The situation of 

 this nerve accounts for the paralysis of the del- 

 toid muscle which sometimes follows dislo- 

 cation of the head of the humerus into the 

 axilla. 



Lymphatic glands are found in great num- 

 bers in the axilla; some are scattered over 

 the internal wall, but there the majority of them 

 will be found in a chain along with the external 

 mammary, or thoracica longior artery. On the 

 posterior wall they form a chain also, in the 

 course of the subscapular vessels. Some will 

 be seen above the lesser pectoral, and several 

 along the axillary vein. Round this last vein 

 we see numerous lymphatic vessels twining. 



When the clavicle has been detached from 

 its connexion with the trunk, and along with 

 the scapula raised from the side, the scrratus 

 magnus may be seen to form the greater part of 

 the internal wall, but extending far below it. 

 This is a flat irregularly quadrilateral muscle ; 

 one surface of it is in contact with the side of the 

 thorax ; the other, looking externally, touches 

 the subscapular muscle, the axillary vessels and 

 nerves, the two pectorals, the latissimus dorsi, 

 and the integuments. The anterior edge pre- 

 sents a convexity forwards, and consists of digi- 

 tations or fleshy slips which arise from the first 

 eight or nine ribs. The fibres all run back to 

 the posterior margin of the scapula, along the 

 whole of which they are inserted. 



The thoracic surface of the muscle, which 

 may be seen by cutting through the trapezius 

 and rhomboid muscles, and pulling out the 

 base of the scapula from the ribs, rests on 

 loose cellular tissue, which connects it with 



