123 The Collar Bone, &V. [Book IX. 



fide of the fternum and the acromion of the fcapula. 

 Its figure is Ibraewhat like that of the lettery*j and it 

 received its name from a fuppofcd refemblance to the 

 key ufed among the ancients. The clavicle, as well 

 as other long cylindrical bones, is larger at its ends 

 than at its middle. The end next the ilernum is trian- 

 gular: the angle behind is confiderably protruded, to 

 form a fnarp ridge, to which the tranfverfe ligament, 

 extended from one clavicle to the other, is fixed. It 

 is for the moft part convex without, and concave within. 

 One end of the clavicle is connected by a ball and 

 focket with the (lernum, and the other by cartilage td 

 the acromion of the fcapula. Its ufcs are to fupport 

 the (boulder and other parts of the fuperior extremity, 

 j:o protect fome large veflels in their pafiage to the 

 arrn, and to connect the fcapula to the thorax. 



The os brachii, or as it is fometimes called the 

 OS humeri, is a cylindrical bone, the round head of 

 which is received into the glenoid cavity of the fcapula. 

 It is larger and rounder at its upper part, and fmaller 

 and flatter below. It has three projecting lines, and 

 as many flat furfaces, by which form it admits of a 

 more advantageous and extenfive connexion of mufcles, 

 than if it had been a fimple cylinder, which is not 

 the cafe with any bone of the body, though all the long 

 bones approach to that form. This bone has many cir- 

 cumftances of ftructure in common with the os femoris. 

 Like that bone it is articulated by a round head, which 

 is furrounded by a capfular ligament, and, like it, has 

 proceflfes for the connexion of mufcles j but thefe pro- 

 cefTes are much lefs remarkable in the os humeri than 

 in the os femoris. At the lower extremity of this 

 bone we cbferve feveral procefles and cavities. The 

 mod remarkable procerTes are the two condyls ; of thefe 

 the external is -the fmalleft, and is of an irregular ob- 

 long 



