160 THE STERNUM. 



ninth, and tenth, are connected to the former, and to each other 

 by firm ligaments. 



The eleventh, and sometimes the tenth rib, has no tubercle 

 for its articulation with the transverse process of the vertebra, 

 to which it is only loosely fixed by ligaments. The fossa, in its 

 lower edge, is not so deep as in the upper ribs ; because the 

 vessels run more towards the interstice between the ribs. Its 

 front end is smaller than its body ; and its short small cartilage 

 is but loosely connected to the cartilage of the rib above. 



The twelfth rib is the shortest and straightest. Its head is 

 only articulated with the last vertebra of the thorax ; and 

 therefore is not divided into two surfaces. This rib is not 

 joined to the transverse process of the vertebra, and therefore 

 has no tubercle, being often pulled necessarily inwards by the 

 diaphragm, which an articulation with the transverse process 

 would not have allowed. The fossa is not found at its upper 

 edge, because the vessels run below it. The forepart of this 

 rib is smaller than its middle, and has only a very small pointed 

 cartilage fixed to it. To its whole internal side the diaphragm 

 is connected. 



The Sternum 



Is the broad flat bone, in the front part of the thorax. In 

 adults it is composed of three pieces, which easily separate 

 after the cartilages connecting them are destroyed. The two 

 lower pieces are frequently found intimately united ; and very 

 often, in old people, the sternum is a continued bony substance 

 from one end to the other ; though we still observe two, some- 

 times three, transverse lines on its surface ; which are marks of 

 the former divisions. 



The sternum, considered as one bone, is broadest and thickest 

 above, and smaller as it descends. The internal surface of this 

 bone is somewhat concave for enlarging the thorax : but the 

 convexity on the external surface is not so conspicuous, because 

 the sides are pressed outwards by the true ribs ; the round 

 heads of whose cartilages are received into seven smooth pits, 

 formed in each side of the sternum, and are kept firm there by 



TMliLi:. 



