228 DISSECTION OF THE UPPER LIMB. 



boundary of the space, the small internal cutaneous nerve of the musculo- 

 spiral should be looked for near the great vessels. 



The large nerves of the brachial plexus are then to be defined. The 

 smallest of these, which possibly may be destroyed, is the nerve of Wris- 

 berg : it lies close to the hinder edge of the axillary vein, and joins with 

 the intercosto-humeral nerve. 



When cleaning the serratus muscle on the ribs the student is to seek 

 on its surface the posterior thoracic nerve ; and to trace the posterior off- 

 sets of the intercostal nerves crossing the axilla. 



THE AXILLA. 



The axilla is the hollow between the arm and the chest (fig. 69). It is 

 somewhat pyramidal in form, and its apex is directed upwards to the root 

 of the neck. The space is larger near the thorax than at the arm, and its 

 boundaries are as follows : 



Boundaries. In front and behind the space is limited, by folds, which are 

 constructed by the muscles passing from the trunk to the upper limb. In 

 the anterior fold are the two pectoral muscles, but these take unequal shares 

 in its construction, in consequence of the difference in their size and shape : 

 thus the pectoralis major A extends over the whole front of the space, 

 reaching from the clavicle to the lower edge of the anterior fold ; whilst 

 the pectoralis minor B, which is a narrow muscle, corresponds only with 

 the middle third of the s'pace. In the posterior boundary, from above down- 

 wards, lie the subscapularis F, the latissimus dorsi muscle D, and the teres 

 major E : this boundary reaches further out than the anterior, especially 

 near the humerus ; and its lower margin, which is formed by the latissimus 

 dorsi, projects forwards beyond the level of the subscapularis. 



On the inner side of the axilla lie the first four ribs, with their inter- 

 vening intercostal muscles, and the part of the serratus magnus c taking 

 origin i'rom those bones. On the outer side the space has but small di- 

 mensions, and is limited by the humerus and the coraco-brachialis and 

 biceps muscles (G and H). 



The apex of the hollow is situate between the clavicle, the upper mar- 

 gin of the scapula, and the first rib; and the forefinger may be introduced 

 into the space for the purpose of ascertaining the upper boundaries, and 

 the depth. The base or widest part of the pyramid is turned downwards, 

 and is closed by the thick aponeurosis reaching from the anterior to the 

 posterior fold. 



Contents of the space. In the axilla are contained the axillary vessels 

 and the brachial plexus, with their branches ; some branches of the inter- 

 costal nerves ; together with lymphatic glands, and a large quantity of 

 loose areolar tissue and fat. 



Position of the trunks of vessels and nerves. The large axillary artery 

 (a) and vein () cross the outer portion of the space in passing from the 

 neck to the upper limb. The part of each vessel now seen lies close to 

 the humerus, reaching beyond the line of the anterior fold of the arm-pit, 

 and is covered only by the common superficial coverings, viz., the skin, 

 the fatty layer or superficial fascia, and the deep fascia. Behind the 

 vessels are the subscapularis (F) and the tendons of the latissimus and 

 teres muscles (D and E). To their outer side is the coraco-brachialis 

 muscle (G). 



