THE CLAVICLE. 87 



cular attachment of the sterno-cleido-mastoid muscle. The anterior surface opposite 

 the outer curve is reduced to a mere rough border, from which the deltoid muscle 

 takes origin ; but in the inner half of its extent it is broadened out into an uneven 

 space, more or less distinctly separated from the inferior surface, and giving attach- 

 ment to the pectoralis major muscle. The poster tor surface is broadest at the inner 

 extremity, and smooth in the whole extent of the internal curvature ; but towards 

 its outer extremity it forms a thick border which gives attachment to the trapezius 

 muscle. About the middle of this surface is the aperture of a small canal for the 

 medullary artery, directed outwards. On the inferior surface, at the sternal end is a 

 rough impression for the attachment of the rhomboid ligament, by which the clavicle 

 is bound down to the first rib ; more externally is a groove, extending somewhat 



Fig. 86. RIGHT CLAVICLE, FROM BELOW. (Drawn by T. W. P. Lawrence.) f 



beyond the middle third of the bone, in which the subclavius muscle is inserted ; 

 behind this, projecting on the posterior border at the junction of the middle and 

 outer thirds, is a well-marked eminence, the conoid tubercle, to which the conoid 

 division of the coraco-clavicular ligament is attached, and from which the rough, 

 generally raised, trapezoid line, for the trapezoid part of the same ligament, is directed 

 outwards and forwards towards the end of the bone. 



The sternal end is the thickest part of the clavicle. It presents a somewhat 

 triangular concavo-convex surface, with its most prominent angle directed down- 

 wards and backwards. The scapular end is broad and flat, and articulates by a small 

 oval surface with the acromion. 



The clavicle is subcutaneous to a greater or less extent in. its whole length ; the 

 most prominent part is about the centre, corresponding to the intermuscular intervals, 

 above between the sterno-mastoid and trapezius, and below between the pectoralis 

 major and deltoid (supra- and in fmclavicular fossae). The outer extremity is a little 

 higher than the upper surface of the acromion against which it fits, and forms a 

 prominence on the upper part of the shoulder. 



The interior of the clavicle contains coarse cancellated tissue in its whole extent, the 

 principal lamellae being directed longitudinally. The shell of compact tissue is for the most 

 part very thick and dense, but it thins out gradually at the two ends of the bone. 



Varieties. At the inner part of the deltoid impression there is sometimes a flattened 

 projection known as the deltoid tubercle: A small foramen for one of the supraclavicular 

 nerves is occasionally found at the fore part of the upper surface of the bone about the 

 middle. 



THE SCAPULA. 



The scapula is placed upon the upper and back part of the thorax, and forms 

 the posterior part of the shoulder-girdle. It is not attached directly to the trunk, 

 but is articulated with the outer end of the clavicle, and from it is suspended the 

 humerus in the shoulder-joint. 



