1416 



CLINICAL AND TOPOGRAPHICAL ANATOMY 



below the groove (musculo-spiral) for the radial (musculo-spiral) nerve, reaching 

 to each intermuscular septum, and tapering away above as high as the teres major. 

 Most of the fibres of this head lie deeply. The lateral head, arising above the 

 groove as high as the great tuberosity, appears in strong relief just below the 

 deltoid; while the middle or long head, arising from the scapula just below the 

 glenoid cavity, appears between the teres muscles. The tendon of insertion, 

 passing into the upper and back part of the olecranon over a deep bursa, is shown 

 by a somewhat depressed area. On the lateral side, an important expansion to 

 the fascia over the anconeus is given off. 



Fig. 1134. — The Elbow-Joint, as Shown by the Rontgen-rays. 



In the ossification of the humerus the epiphyses are of first importance. The upper, 

 con.si.stinK of those for the head and two tuhorositios, which form one about the seventh year, 

 blends with the shaft between the twentieth and twenty-fifth years. Separation usually takes 

 place at an earlier date, this beinf; explained by the fact that the cone-like arrangement by which 

 the diaphysis fits into the cap of the epiphysis bcconn's more nuarkcnl toward the date of union, 

 and thus tends to prevent displacement. (Thomson.) The lower epiphysis. The condition 

 of this varies with the degree of coales(rence of its four centres. The first and chief, that for the 

 capitulum (second or third J'car), unites with tliose for the trochlea and lateral epicondyle soon 

 after puberty, and forms an epiphysis which joins with the shaft at about sixteen. The epi- 

 physis for the medial epicondyle appears at the fifth year and \inites with the shaft at the 

 eighteenth. Injury to this epiphysis may damage the ulnar nerve and open the elbow-joint. 

 Thus, at and after puberty, there are two chief cijiiphyses to remember here: — (a) the larger, 

 consisting of cajjituhir, trochlear, and lateral epicf)Mdyle c-(>ntres. This is almost entirely intra- 

 articidar; (/;) the smaller, that for the media! epicondyle; tlie extent to whicli this is intra-artic- 

 ular varies. The structures that would be divided in an amputation at the centre of the arm 



