26o HUMAN ANATOMY. 



comparative rarity : ( i ) because of the elastic curves of the bone, which enable 

 it to escape fracture in many cases of direct violence ; (2) because of the inter- 

 position of the subclavius muscle between the bone and the nervous and vascular 

 trunks ; (3) because of the situation of the common fracture, the inner end of 

 the outer fragment ( the portion most likely to inflict injury) being both above and 

 external to \he region of danger. Still, cases of wound of the subclavian vessels, 



iniernal jugular vein, and of pressure pa- 

 P^ g ralysis of the upper extremity have been 



reported as complications of fracture of 

 the clavicle. 



The supraclavicular nerves (branches 

 of the third and fourth cervical) pass in 

 front of the bone, and may be involved in 

 the callus, giving rise to severe and per- 

 sistent pain. 



In resection or excision of the clavi- 

 cle, either for disease or as a step in the 

 performance of an interscapulo-thoracic 



Lines of fracture of the clavicle and acromion process. amputation, the protection afforded the 



vessels by the subclavius muscle should 

 be remembered. Superficially, the cephalic vein and the supraclavicular nerves may 

 have to be divided. 



Disease of the clavicle is not uncommon as a result of the various infections, — 

 syphilitic, tuberculous, typhoidal, etc. The bone is also the subject of new growths, 

 especially of sarcomata. The anatomical relations already alluded to are those chiefly 

 involved in these cases. 



Swelling and oedema of the arm may result from pressure on the subclavian 

 vein in the angle between the clavicle and the rib ; gangrene, from pressure upon 

 the artery ; pain or paralysis, from pressure upon the brachial plexus at the outer 

 part of the costo-clavicular space. It is probable that, in view of the subcutaneous 

 position of the clavicle and its consequent exposure to slight traumatisms, osteitis of 

 one form or another would be more frequent if it were not for its great elasticity, 

 which probably limits the effect qf minor blows to the superficies of the bone. Ac- 

 cordingly, syphilitic subperiosteal nodes are fairly common, while tuberculosis and 

 septic and post-typhoidal osteitis are relatively rare. 



Landmarks. — The clavicle is subcutaneous through its entire length. When 

 at rest the bone is about on the same level as the spine of the scapula. In inspira- 

 tion it moves forward an inch. 



The. inner end of the bone is its largest portion, and its projection in front of 

 and above the clavicular notch on the sternum should not be erroneously regarded 

 as evidence of disease or injury. The deltoid tubercle at its outer third is sometimes 

 unusually prominent, and should not then be mistaken for an exostosis. 



The curves of the bone may easily be traced from end to end. The normal 

 curves may be increased in greenstick fracture without any positive angularity being 

 produced ; but in this case careful measurement will show that the distance between 

 the two ends of the bone is slightly lessened as compared with the uninjured side. 

 It should not be forgotten, however, that the curves are apt to be increased in mus- 

 cular persons, and that for the same reason the right clavicle is sometimes more 

 curved, thicker, and a little shorter than the left. 



In general terms it may be said that the inner third of the bone is in relation 

 below to the first rib, which it crosses obliquely ; the middle third to the axillary 

 vessels and the brachial plexus (and below them to the first intercostal space); and 

 the outer third to the coracoid process and the acromio-clavicular joint (Fig. 274). 

 In the male, and in robust, vigorous persons generally, the clavicles are on a high 

 plane and pass almost horizontally outward, giving the " square-shouldered " appear- 

 ance usually associated with ideas of muscular strength and decreasing the apparent 

 length of the neck. In the strong male the outer end may even be higher than the 

 inner. 



In narrow-chested and in consumptive persons the clavicles are depressed and 



