AXILLA. 



359 



Immediately under the skin we find some 

 cellular substance, containing a small quantity 

 of fat ; and next a fascia of considerable thick- 

 ness, which gradually loses itself on the side of 

 the thorax, in the general superficial fascia of 

 the trunk. It will be found extremely variable 

 in different subjects, according to the embon- 

 point of the individual, sometimes loaded with 

 fat, at other times thin, firm, and somewhat 

 aponeurotic, with its principal bands stretched 

 across from the anterior to the posterior wall of 

 the axilla. In raising it, layer after layer may 

 be removed, until it opens up into that ex- 

 tremely lax cellular tissue which attaches itself 

 to the walls of the axilla, loosely supporting 

 glands, vessels, and nerves, and permitting all 

 the motions of which this part is capable. It is 

 obviously cellular membrane. When enlarged 

 glands, or abscesses, or tumours of any kind, 

 form under it, it readily yields, and stretches 

 before the distending force, never exerting any 

 painful pressure on them. The cellular tissue 

 under it is very loose. Numerous vessels ra- 

 mify through it which are chiefly derived from 

 the thoracica alaris artery. These vessels are 

 occasionally ruptured, when extensive ecchy- 

 moses ensue. Matter formed here passes 

 easily from one part to another, and gives rise 

 to obstinate sinuses, not easily remedied on 

 account of their length and tortuous course. 



On carefully removing the dense cellular 

 membrane of the floor, and that more loose 

 tissue which it conceals, the edges of the 

 axillary folds will be seen. Close to the an- 

 terior of them we observe the thoracica longior 

 artery, with its accompanying veins and several 

 lymphatic glands, and, under cover of the 

 posterior, the subscapular vessels and nerves ; 

 whilst a great bundle of arteries, veins, and 

 nerves, with the biceps and coraco-brachialis 

 muscles, stretch along the humerus. To this 

 view of the parts the operating surgeon will 

 look with peculiar interest. It is from below 

 that we generally operate on the axilla, and the 

 three sets of vessels just now mentioned con- 

 stitute the most important subjects for consi- 

 deration when the scalpel is to be used. It is 

 obvious that free incisions may be practised in 

 the centre of this space or upon its thoracic 

 side, but that all its other boundaries are beset 

 with dangers. 



To follow up the anatomy of this region with 

 advantage, each of its walls must be examined 

 in detail. The anterior wall consists of the 

 pectoralis major and minor muscles. The 

 pectoralis major is a large flat muscle, of a tri- 

 angular shape, extending over the front of the 

 thorax, from the clavicle and sternum to the 

 humerus. 



The origin of this muscle is curved, its con- 

 vexity being directed upwards and inwards; this 

 may be called its base. The insertion or apex 

 is outwards and downwards. One surface 

 looks outwards and forwards, the other back- 

 wards and inwards. The inferior margin extends 

 from the seventh rib to the humerus and is nearly 

 horizontal, folded on itself and free. The outer 

 edge is nearly vertical, at first about an inch dis- 



tant from the deltoid, but soon coming into con- 

 tact with it, and so continuing to its insertion. 



The triangular space between the deltoid 

 and pectoral may be seen even in the living 

 person when the shoulders are shrugged up, 

 especially if the individual be thin. It is in this 

 situation that the axillary artery commences, and 

 might be cut down upon without dividing any 

 muscular fibres except those of the platysma ; 

 it is however protected by the costocoracoid 

 ligament, and by the edge of the pectoral mus- 

 cle. In this interval we see the cephalic vein 

 and a small artery, the thoracica humeraria, 

 which is the descending branch of the thoracica 

 acromialis. The cephalic vein is derived from 

 a plexus on the outer and back part of the 

 hand. After various communications in its 

 superficial course it gets between the deltoid 

 and pectoral muscles, and on arriving at the 

 triangular interval above mentioned, it dips in 

 under the edge of the great pectoral and just 

 above the lesser, to empty itself into the axillary 

 vein. 



When the pectoralis major has been raised, 

 we bring into view a stratum of cellular tissue, 

 in which several branches of the thoracica 

 suprema artery and some nervous filaments 

 ramify before they enter the muscles. Under- 

 neath this tissue lies the pectoralis minor, still 

 concealing the cavity of the axilla. 



The posterior surface of the great pectoral is 

 riot nearly so extensive as the anterior ; its fibres 

 arise from the cartilages of the ribs, and, there- 

 fore, the extreme limit of the axilla in front is not 

 to be estimated by the superficial dimensions of 

 the muscle. A line drawn oblique'y downwards 

 and outwards, beginning one inch outside the 

 sterno-clavicular articulation, and ending an inch 

 outside the nipple, will nearly mark the junction 

 of the anterior and internal walls. 



This muscle is sometimes torn across by ex- 

 ternal violence. We have seen this occasioned 

 by the passage of a railway carriage over it, 

 and marked by a deep depression, but without 

 any laceration of the integuments. 



The pectoralis minor is shaped like the major, 

 but it is considerably smaller. Its base is ap- 

 plied to the ribs, its apex to the coracoid pro- 

 cess of the scapula. One surface is turned 

 outwards and forwards to the greater pectoral, 

 the other back to the axilla. Attached on the 

 one hand to the upper edge and the external 

 surface of the third, fourth, and fifth, and some- 

 times the second, true ribs, near their cartilages, 

 by so many distinct slips, (hence its occasional 

 name serratus minor anticus,) and an aponeu- 

 rosis which covers the intercostal muscles, it 

 terminates in a flat tendon which is inserted into 

 the inner border of the coracoid process near its 

 apex. In this situation it is intimately con- 

 nected with the coraco-brachialis and short head 

 of the biceps, sometimes sending fibres to be 

 continuous with the triangular or coraco-acromial 

 ligament, and in some rare instances the entire 

 tendon runs across the coracoid process, and 

 through this ligament to join the capsular liga- 

 ment of the shoulder-joint. The tendon is 

 about an inch broad ; very short on the posterior 



