66 



Anatomy of Skeleton 



The shaft (Fig. 50) has on its lower aspect, just external to and behind the costal 

 facet, a rough rhomboid impression for the rhomboid ligament : outside this, the 

 groove for the Subclavius muscle, bounded by ridges that give attachment to thexosto- 

 coracoid membrane : close to the back margin of its outer third a prominent conoid 

 tubercle for the conoid ligament, and running outwards and forwards from this a ridge 

 for the trapezoid ligament. 



The upper surface of the shaft is comparatively smooth. On the inner third is 

 the origin of Sterno-mastoid. An area for Pectoralis major occupies the front and 

 lower aspect of the inner half of the bone. The Trapezius and Deltoid are attached 

 to the back and front margins respectively of the outer third, and in the area of the 

 last-named muscle a small deltoid tubercle may be apparent. 



The outer end presents a narrow articular surface for the acromion, bevelled so 

 that it looks downwards and outwards, with the result that the bone tends to ride 

 above the acromion : it is normally on a higher level, and the direction of the articular 



Lauer aspect 



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 end 



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FIG. 50. Left clavicle from below and from above. To tell right from left, have the 

 subclavian groove below, the flat end externally, and the rhomboid and conoid 

 impressions towards the back. 



surface accounts for the difficulty in retaining the clavicle in place after dislocation 

 at this joint. There are feeble ligamentous markings round the articular surface. 



The inner end of the bone is separated from the sternum by a disc of interarticular 

 nbro-cartilage, which is thinnest in the centre and may be perforated here. 



The disc has strong attachment, as shown in the diagram (Fig. 52), by its back 

 and upper part to the clavicle and at its lower part to the sternum and first costal 

 cartilage, so that it forms a band of connection between this part and the clavicle ; 

 but it must not be forgotten that the meniscus is also fastened round its periphery to 

 the capsule of the composite joint, thus completely dividing the joint cavity into two 

 save when it is perforated. The strong attachment to the clavicle above is associated 

 with this capsular connection, because the capsule here is thickened and strengthened 

 by the interclavicular ligament : the marking for this ligament can be recognised on 

 the bone above and behind the articular surface. 



The mechanical result of such fixation of the meniscus is that the clavicle is held 

 down to the sternum and is kept from riding over its top edge, while at the same time 

 the bone can be elevated and depressed, rotating round an antero-posterior axis 

 passing through the attachment of the fibro-cartilage. The elevation of the clavicle 

 on this axis must be accompanied by a sliding out of its lower surface on the costal 

 cartilage, whence the necessity for the lower articular surface. The elevation is 



