AXILLARY SPACE 13 



different directions as they proceed to join both laminae of 

 the tendon of insertion ; thus the superior fibres descend 

 slightly, the intermediate fibres pass horizontally, whilst the 

 inferior fibres ascend, and, at the same time, gain the deep 

 surface of the rest of the muscle. A smooth, full, and rounded 

 lower border is in this way formed which constitutes the 

 anterior fold of the axilla. The precise manner in which 

 the muscle is attached to the humerus will be more fully 

 studied at a later stage of the dissection (p. 56). 



The pectoralis major is supplied by the medial and lateral 

 anterior thoracic nerves. 



Axilla. The axilla may be defined as being the hollow or 

 recess between the upper part of the side of the thorax and 

 the upper part of the arm. When the limb is abducted 

 from the trunk, and the areolo-fatty tissue which occupies 

 the axilia is removed, the 'space presents a pyramidal form. 

 The apex, or narrow part of the space, placed immediately to 

 the medial side of the coracoid process, is directed upwards 

 towards the root of the neck, whilst the wider part or base 

 looks downwards. The medial wall formed by the thorax is 

 of greater extent than the lateral wall formed by the arm. 

 It follows from this, therefore, that the anterior and posterior 

 walls converge as they proceed laterally, and because the 

 posterior wall is longer than the anterior, the posterior border 

 of the base is lower than the anterior. 



Before engaging in the dissection of the space, it is necessary that the 

 student should have some knowledge of its boundaries, and the manner 

 in which its contents are disposed in relation to these. 



Boundaries of the Axilla. The anterior wall is formed by 

 the two pectoral muscles and the costo-coracoid membrane. 

 The pectoralis major constitutes the superficial stratum, and 

 is spread out over the entire extent of the anterior wall. 

 The pectoralis minor, which lies subjacent to the pectoralis 

 major, is only in relation to about one-third of the anterior 

 boundary, whilst the interval or gap between this muscle and 

 the clavicle is filled up by the costo-coracoid membrane. 

 The lower border of this wall of the axilla is the anterior 

 fold of the axilla. It is formed by the lower margin of the 

 pectoralis major, strengthened, medially, by a small part of 

 the lower border of the pectoralis minor, which comes into 

 view near the side of the thorax. 



The posterior wall of the axilla is somewhat longer than 



