The Axilla. 35 



occasions I have found the posterior lamella formed by 

 the deep fibres only, the rest of the muscle forming the 

 anterior lamella. This arrangement serves a useful pur- 

 pose in elevating the arm, for, if the muscle were inserted 

 in the usual manner, i.e., if there were no twist, it would 

 be impossible to raise the arm beyond a right angle, be- 

 cause the lower fibres would allow only a limited amount 

 of elevation, but, with the twisting, the lower fibres being 

 inserted higher up on the humerus than the upper, 

 steady the head of that bone just as the biceps does, 

 and thereby assist the upper fibres, which are inserted 

 lower down, in raising the arm. From the insertion 

 of the anterior lamella a band of fascia is sent to 

 join the deep fascia of the arm and, from the 

 posterior lamella, another band is prolonged upwards 

 over the biceps tendon holding it in position in the 

 groove. 



Other actions of the pectoralis major are : anterior 

 adduction, i.e., drawing the arm inwards and forwards 

 across the chest, and slight inward rotation of the 

 humerus. Acting from below, it raises the body and, 

 with the arm fixed, act? as a muscle of forced respiration. 



The function of the pect. mino? arising from the 3rd, 

 4th and 5th ribs near their cartilages and inserted into the 

 inner border of the coracoid, is to draw the shoulder down- 

 wards, forwards and inwards. The latter action, i.e. in- 

 wards, is very limited unless the clavicle be broken, since 

 this bone acts as an outrigger and keeps the scapula at a 

 definite distance from the sternum, hence this inward 

 movement of the shoulder from the action of the pect. 

 minor is produced by rotation of the scapula at the acro- 

 mio-clavicular articulation. The serratus magnus carries 

 the scapula i.e. the shoulder forward and causes rota- 

 tion of this bone at the acromio-clavicular articulation, 



