26 



EOXES Ob' ■LllK TilOllAX. 



The prosieminn is the thickest part of the bone. Its anterior snr- 

 face presents a slignt median elevation, its posterior is smooth and 



Fio-. 22. 



Fig. 22. — The Sternuh of a middle-aged 

 Man. (A. T.) i 



A, from before, 1, 2, 3, 4, 5, 6, & 7, tlie 

 articular surfaces for the corresponding 

 costal cartilages ; S, manubrium or upper 

 piece, still separate from the body ; 9, 

 middle of the body ; 10, ensiform por- 

 tion, os.seous, and united to the body ; 11, 

 inter-clavicular notch • 12, articular notch 

 for the clavicle. 



B, the same sternum viewed from the 

 riglit side, showing the general convexity 

 of the bone forwards. The different facets 

 of articulation of the clavicle and costal 

 cartilages will be distinguished by their 

 position in comparing the figure B. with A. 



somewhat concave. Its npper bor- 

 der is divided into three deep 

 notches ; the middle one is named 

 the incisiim semilunaris, or infcr- 

 cJavicular notch ; the lateral ones 

 fonn two depressed articular sur- 

 faces directed upwards and out- 

 wards, for articulation with the 

 clavicles. Each lateral border pre- 

 sents superiorly close to the clavi- 

 cular surface, a rough triangular sm'face, which miites with the cartilage 

 of the first rib. Below this the bone slopes inwards, and at its inferior 

 angle presents a small surface, which with a similar one on the meso- 

 sternum forms a notch for the cartilage of the second rib. The lower 

 margin is straight and united by intervening cartilage to the upper 

 margin of the mesostemum. 



The mesosfemiwi is marked on its anterior surface by three slight 

 transverse elevations at the lines of junction of its four component 

 j)arts. Its posterior surface is comparatively smooth. Each lateral 

 margin presents five notches for the reception of costal cartilages, and 

 a small surface superiorly, which, with the similar depression on the 

 presternum, forms the notch for the second costal cartilage. The 

 notches for the third, fourth, and fifth costal cartilages are opposite the 

 lines of junction of the foiu' segments of the body of the sternum ; 

 those of the sixth and seventh are placed close together on the sides of 

 the inferior segment, that for the seventh being frequently completed 

 by the ensiform cartilage. The lower part of the presternum is some- 

 times pierced in the middle line by a considerable hole. 



The meiastcrmini, ensiform process, or xjiphisternum, is a thin spatula- 

 like process projecting downwards between the cartilages of the seventh 

 ribs. It is subject to frequent varieties of form ; being sometimes bent 

 forwards, sometimes backwards, often forked, and sometimes perforated. 



The ptemtim i^« pubjccfc to many varieties. It is sometimes divided vertically in 

 the whole or part of its length. It is not unfreqnently much shoiter than usual, 



