Limbs: Upper Limb 71 



inner and outer thick borders, marked by Pectoralis minor internally, and by coraco- 

 acromial and coraco-humeral ligaments externally, and a rough upper surface, which 

 presents a prominent conoid tubercle for conoid ligament behind, and, outside and in 

 front of this, roughnesses for trapezoid ligament : further forward part of Pectoralis 

 minor insertion, and, at the tip, origin of Coraco-brachialis and short head of Biceps. 

 At the base of the process, just above the glenoid cavity, is the bicipiial or supra- 

 glcnoid tubercle for the origin of long head of Biceps. The neck is sometimes termed the 

 anatomical neck, lying outside the coracoid, and the term surgical neck is applied 

 to the area crossed by a line drawn from below the glenoid to the notch internal to the 

 coracoid. The lines of both these " necks " pass between the glenoid rim and the free 

 border of the spine : the notch between the rim and spine is sometimes termed the 

 great scapular notch. 



The acromion lies above and rather behind the glenoid fossa, and does not come 

 so far forward as the coracoid process : about an inch and a half separates the tips 

 of the two processes. The upper surface of the acrormoh and the back surface of the 

 spine are continuous and subcutaneous. 



Ventral Surface. 



Observe that the narrow rim on this surface close to the vertebral border, for the 

 Serratus magnus, widens at the upper and lower angles especially at the lower angle 

 and thus the origin of Subscapularis cannot reach these or the intervening border. 

 These widenings correspond with the arrangement of the digitations of the muscle : 

 the upper two are inserted into the upper angle, the next two into the border, and the 

 remaining ones converge on the lower angle. The arrangement indicates that the 

 main action of the muscle is on the lower angle, and such action is illustrated in the 

 movement of raising the hand over the head. The arm is abducted by the fibres of 

 the Deltoid acting from the outer margins of the acromion, and the effect of the con- 

 traction of this muscle is to approximate its points of attachment either by raising the 

 arm or by rotating the scapula inwards on its upper attachments (Fig. 60). Naturally 

 the latter movement would occur rather than the lifting of the heavy limb, if it were 

 not for the Serratus magnus, which, pulling forward on the angle of the scapula, would 

 tend to rotate that bone outwards and thus to neutralise the action of the Deltoid on 

 the bone Thus the Serratus can be said to fix the scapula while the Deltoid raises 

 the arm to a~nght angl<- : after this, since the humerus cannot be further abducted 

 from t lie scapula < >\ving to the conformation of the tissues, the Deltoid fixes the humerus 

 qn_the scapula while the Serratus magnus, by its active contractions, rotates the scapula 

 outwards and thus raises the arm higher : the Trapezius is associated with Serratus 

 magnus in llie-e actions, whereas the Rhomboids have the opposite effect when they 

 contract. 



Such action of the Serratus magnus on the scapula is best served by concentrating 

 its force on the lower angle, as far as possible from the axis of rotation, and this calls 

 for a modification in the structure of the scapula. It is evident that, with a weight 

 tending to turn the glenoid cavity down on the one hand and a strong muscle pulling 

 the angle forward and thus turning the glenoid up on the other hand, the bone requires 

 strengthening in the line between the angle and the glenoid, for here is where it would 

 " buckle " at once if it lacked resisting power. Consequently we find a very t 

 bar of bone in this line of greatest strain, more apparent on the ventral side owing 

 to its concavity, but also visible dorsally where it is covered by the Teres muscles. 



This thick ventral bar, then, is a " primary " ridge, concerned in the mechanic 

 building of the bone, and has nothing to do with the axillary border, which is a secondary 



