206 



OSTEOLOGY. 



HEAD 



ANATOMICAL 

 NECK' 



DELTOID TUBEROSITY 



tubercle) abuts on the lateral side of the head and becomes continuous with the 

 body distally. Its proximal surface forms a quadrant, which is subdivided into 



three more or less smooth areas of un- 

 equal size. Of these the upper and an- 

 terior is for the insertion of the supra- 

 spinatus muscle, the middle for the infra- 

 spinatus, whilst the most distal and 

 posterior serves for the insertion of the 

 teres minor muscle. The lateral surface 

 of this tubercle, which bulges beyond the 

 line of the shaft, is rough and pierced by 

 numerous vascular foramina; Anteriorly 

 the greater tubercle is separated from the 

 tuberculum minus (lesser tubercle) by a 

 well-defined furrow, called the sulcus 

 intertubercularis (intertubercular groove) 

 (O.T. bicipital groove). The transverse 

 numeral ligament stretches across the 

 groove between the two tubercles, thus 

 converting the groove into a canal in 

 which the tendon of the long head of 

 the biceps and the ascending articular 

 branch of the anterior circumflex artery 

 of the humerus are lodged. The lesser 

 tubercle lies in front of the lateral half of 

 the head ; it forms a pronounced eleva- 

 tion, which fades into the shaft distally. 

 The surface of this tubercle is faceted 

 above and in front for the insertion of 

 the subscapularis muscle, whilst laterally 

 it forms the prominent medial lip of the 

 inter-tubercular groove. Distal to the 

 head and tubercles the shaft of the bone 

 rapidly contracts, and is here named the 

 collum chirurgicum (surgical neck) owing 

 to its liability to fracture at this spot. 



The corpus burner! (body, or shaft) 

 is cylindrical in its proximal half. On it 

 the inter-tubercular groove may be traced 

 distally and slightly medially, along its 

 anterior surface. The edges of the groove, 

 which are termed its lips, are confluent 

 proximally with the greater and lesser 

 tubercles, respectively. Here they are 

 prominent, and form the cristae tuberculi 

 majoris et minoris (crests of the greater and 

 lesser tubercles). Distally the lips of 

 the intertubercular groove gradually 

 fade away, the medial more rapidly than 

 the lateral, which latter may usually be 

 traced distally to a rough elevation 

 placed on the lateral anterior surface of 

 the shaft about its middle, called the 

 deltoid tuberosity. Into the lateral lip 

 of the intertubercular groove are in- 

 serted the fibres of the pectoralis major 

 tendon ; hence it is sometimes described 

 as the pectoral ridge. To the floor of the groove the latissimus dorsi is attached ; 



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OLECRANON 

 KOSSA 



MEDIAL 

 EPICONDYLE 



GROOVE 



ULNAR NERVE 



GROOVE FOR RADIAL 

 NERVE 



.TERAL' 

 EPICONDYLE 



TROCHLEA 

 FIG. 196. POSTERIOR SURFACE OF THE RIGHT HUMERUS. 



