Limbs : Upper Limb 83 



The insertion of the Subscapularis also comes down well below the small tuberosity 

 on to the shaft, and may here be either muscular or tendinous, with absence or presence 

 of a corresponding marking. Bearing these facts in mind, it is easy to show the line 

 of capsular attachment on the bone (Figs. 63 and 68). Starting behind, it passes 

 down close to the inner side of the three facets, so leaving the neighbourhood of the 

 anatomical neck as it runs along the Teres minor. It still passes down along the inser- 

 tion of Teres minor, thus reaching the level of the surgical neck, but 'near the lower 

 end of this insertion the line turns suddenly inwards and forwards along the surgical 

 neck and inclines upwards to come again on to the anatomical neck internal to the 

 Subscapularis on the small tuberosity : it sometimes reaches the lower part of this 

 insertion. So the line passes up to the Supraspinatus facet, but it should be noticed 

 that the inclusion of the coraco-humera] ligament in the capsule has led to the line 

 of humeral attachment of capsule being extended outward on both tuberosities 

 at each side of the upper end of the bicipital groove : thus the coraco- humeral 

 ligament is visible between the Supraspinous and Subscapular tendons (Fig. 62) 

 and covers the issuing tendon of the Biceps, being strengthened here by the trans- 

 verse ligament. 



It is not quite apparent why the capsule and muscles should leave their association with the 

 anatomical neck in the lower part, or why there should be no strengthening tendon below the 

 joint as on the other aspects, but probably all these modifications are connected with the marked 

 downward displacement of the head that occurs when the arm is abducted : at any rate, the lower 

 part of the joint thus becomes its weak point mechanically, and when the arm is abducted the head 

 of the humerus can be fairly easily dislocated downwards, the only resistance being offered by the 

 Supraspinatus tendon. The long head of the Triceps, however, provides some support when the 

 arm is abducted. 



Summing up these observations on the region of the head of the bone, we can 

 obtain a conception of the immediate relations of the capsule (Figs. 57 and 62). It 

 has Subscapularis tendon in front (separating it from Coraco-brachialis, etc.), Supra- 

 spinatus above (separating it from acromion and Deltoid and corresponding bursae), 

 Infraspinatus and Teres minor behind (separating it from Deltoid). Below it the 

 circumflex nerve and vessels run back close to the neck of the bone, in contact 

 with the lower margins of Subscapularis and Teres minor : the long head of 

 Triceps is below and internal, but not in immediate relation, except when the 

 arm is abducted. 



Articulate the bones and observe that the greater tuberosity projects (Fig. 51) 

 far out beyond the level of the acromion. This implies that the tendon of the 

 Supraspinatus passes to its insertion under cover of the Deltoid, and the " subacromial 

 bursa " which intervenes between the tendon and the acromion becomes " sub- 

 deltoid " as it covers it further out, to extend beyond it on to the outer side of the 

 upper and more prominent part of the tuberosity. 



It is a matter of some practical interest to be able to place the upper epiphysial 

 line. This is the " growing end " of the bone, and the upper epiphysis is a compound 

 of three centres, one for each tuberosity and one for the head : these appear within 

 the first few years of life and coalesce at about six years. The epiphysis formed in 

 this way can be marked out as in the figure (Fig. 63), the line passing just below the 

 facets for Teres minor and Subscapularis and just touching the lower lip of the articular 

 surface. It is apparent that the lower third or more of the capsule is attached to the 

 diaphysis, the remainder being on the epiphysis. 



The compound nature of the epiphysis has led to the introduction of the term 

 morphological neck to indicate the true junction of the head and shaft only : this 



62 



