86 CLINICAL APPLIED ANATOMY. 



tendon of the biceps acts as a strap, and, together with the long 

 head of the triceps, prevents the other muscles from causing any 

 alteration in the relationship of the two fractured ends. Separa- 

 tion of the upper epiphysis of the humerus, which is an accident 

 whicli may occur in persons under the age of eighteen, entails a 

 very similar displacement to that mentioned above. The 

 epiphyseal cartilage in general remains attached to the epiphysis 

 rather than to the diaphysis. It is in these two lesions that the 

 circumflex nerve ma} 7 be involved. 



Fracture of the shaft. This commonly occurs about the 

 middle of its length, and may therefore be just above or just 

 below the insertions of the deltoid and the coraco-brachialis. If 

 above these insertions the displacement will be that the upper 

 fragment is drawn inwards by the muscles passing from the 

 trunk to the arm, namely the pectoralis major, and the latissimus 

 dor si, while the lower fragment will be drawn upwards by the 

 deltoid, the biceps, the coraco-brachialis, and the triceps, and 

 slightly outwards by the deltoid. If, however, the line of 

 cleavage is below the insertions of these two muscles, the upper 

 fragment will now be abducted by the deltoid, and the lower 

 fragment is drawn upwards and inwards, to a slight extent by 

 the biceps and the triceps, still further tending to push the 

 lower end of the upper fragment outwards. The intervention of 

 the muscular fibres, which surround the bone in the region of 

 the fracture, between the fragments may effectually prevent union. 

 In some instances these fibres are actually driven into the 

 medullary cavity of the bone. Two other explanations of non- 

 union from an anatomical point of view are also given, one that 

 the nutrient artery which enters the bone near the seat of the 

 fracture is itself liable at the same time to be torn across, and 

 the other that there is apt to be movement at the site of the 

 fragments, when the elbow joint is fixed by the splint adjusted 

 for treatment. 



The musculo- spiral nerve runs a course from within outwards 

 behind the shaft of the bone, lying in a musculo-osseous canal 

 close against the bone itself. Hence it follows that there is a great 



