260 



77/i' II n merits 



, 



THE HUMERUS 



The humerus has seven centres of ossification, that for the shaft 

 appearing very early in foetal life ; the head begins to ossify in the 

 second year, and the tuberosities in the third. The 

 lower end has four centres : for the radial head in the 

 second year, the internal condyle in the fifth year, the 

 trochlear surface in the twelfth, and the external con- 

 dyle in the fourteenth year. 



The nutrient artery, from the brachial, running 

 towards the elbow, shows that the lower epiphysis joins 

 the shaft (at puberty) before the upper (at manhood). 

 But the prominent internal condyle, which begins to 

 ossify early, does not become united until the eighteenth 

 year. 



Fractures. The upper epiphysis may become 

 'unglued' at any time up to manhood, and that from 

 comparatively slight violence at times. There is usually 

 not much displacement, and if a small pad be placed 

 in the axilla, to prevent the pectoralis major, latissimus 

 dorsi, and teres major drawing the shaft inwards, and 

 the arm be fixed to the side, union quickly occurs. 

 The disturbance of the junction-cartilage, however, 

 may interfere with subsequent growth of the bone. 



The surgical neck is slender and 

 is often the seat of fracture ; then if the 

 supra-spinatus be everting the upper 

 fragment, and the muscles of the axil- 

 lary fold be drawing the shaft inwards, 

 and, with the help of the deltoid, biceps, 

 coraco-brachialis, and triceps, upwards 

 as well, there maybe considerable over- 

 lapping of the fragments. 



This is the classic form of the dis- 

 placement, though I venture to doubt 

 if, as is usually described, it is owing 

 to the action of the supra-spinatus that 

 the upper fragment is tilted outwards. 

 Indeed, unless the subscapularis, infra- 

 spinatus, and teres minor were in a 

 conspiracy of silence, how could the 

 Fracture of surgical neck. (GRAY.) supra-spinatus abduct the fragment ? 



The displacement, if any there be 



after the fracture, is as follows : the shaft of the bone is drawn upwards 

 and inwards, as already explained, and its upper end thus lies to the 



