HUMERUS. 



79 



tendon of the biceps muscle : this groove, commencing between the 



tuberosities, descends with an inclination inwards, and is bounded by two 



rough ridges, the external and most prominent of which gives attachment 



to the pectoralis major muscle, the internal or posterior to the latissimus 



dorsi and teres major. Towards the middle of the 



shaft, on the inner lateral line, is a rough linear mark Fig. 70. 



where the coraco-brachialis muscle is inserted, and 



lower down there is a medullary foramen directed 



downwards into the interior of the bone. On the 



external part of the shaft, near its middle, in a line 



anteriorly with the external bicipital ridge, is a large, 



rough, and uneven surface, of a triangular shape, the 



impression of the deltoid muscle. Below this the 



external bicipital ridge is continued into a smooth 



elevation which, descending on the front of the shaft 



to the inferior extremity, separates an external from 



an internal surface, while at the sides two sharp edges, 



the external and internal supracondyloid ridges spring 



from the eminences of the same name and ascend 



for some distance, separating the anterior from the 



flat posterior surface. About the middle of the 



shaft externally, a broad depression, the musculo-spiral 



groove, passes downwards and forwards in a spiral 



direction, limited above by the deltoid impression 



and below by the external supracondyloid ridge, and 



lodges the musculo-spiral nerve and the accompanying 



artery. 



Fig. 70. RIGHT HUMERUS FROM BEHIND. 



1, 3, 8, & 10, the same as in Fig. 69; 15, is placed above 

 the olecranon fossa, 



The inferior extremity is much enlarged laterally, 

 flattened from before backwards, and is curved slightly 

 forwards. Projecting on either side are the external 

 and internal supracondyloid eminences (the condyles of 

 most authors, epicondyle and epitrochlea of Chaussier), 

 the internal of which is much more prominent than 

 the external, and is slightly inclined backwards. The 

 inferior articular surface, fitting by peculiar curved 

 grooves aud eminences to the corresponding surfaces 

 of the radius and ulna, is divided by a ridge into an 

 external and an internal part. The external part, 

 articulated with the radius, consists of a rounded eminence directed forwards, 

 called the capitellum, and a groove internal to it ; it does not extend to the 

 posterior surface. The internal part, the trochlea, articulates with the ulna, 

 and extends completely round from the anterior to the posterior surface of 

 the bone ; it is grooved down the middle like the surface of a pulley, and is 

 somewhat broader behind than in front ; anteriorly, its margins are inclined 

 downwards and inwards ; posteriorly, upwards and outwards, and so that seen 

 from behind, it lies in the middle part of the bone. Anteriorly, the internal 

 margin of the trochlea is the most prominent, and widens below into a 

 convexity parallel to the groove ; posteriorly, the external margin is most 



