Chap. 7;] Articulation of the Spine. 113 



The thorax is a bony cavity, narrow above, wide 

 below, and arched behind and at its fides. 



The fternum or breaft-bone, which forms the an- 

 Kerior part of the thorax, is of a fpongy confidence, 

 and of a fiat and nearly triangular form j in infancy 

 it confifts of many parts, in the adult (late of only- 

 two, or fometimes three. The upper part is broad 

 and thick, the lower narrow and thin. The loweft 

 part of the fternum, from its refemblance to a dag- 

 ger, and its cartilaginous nature, is called cartilago 

 enfiformis. The upper part of this bone is notched 

 for the r afifage of the wind-pipe, and there are two 

 cavities in its fides for the articulation of the cla- 

 vicles or collar-bones. There are alfo feven fmall 

 holes on each fide, for the articulation of feven ribs. 

 Its ufes are to fupport the ribs, to protect the lungs 

 and heart, and to furnifh connection to a mufcuiar 

 organ, which will be afterwards confidered, called the 

 diaphragm. 



The ribs which conftitute the greater part of the 

 cavity of the thorax, are fomewhat of a femicircular 

 form j they pafs from the fpine towards the fternum ; 

 they are not connected, however, to the vertebras 

 themfdves, but to the cartilagino-ligamentous fub- 

 ftance which connects the vertebras to each other. 

 At the pofterior part the rib has two procefies ; one 

 of thefe, by which it is connected between two verte- 

 bras, is called its head ; another is articulated with 

 the tranverfe procefs of the vertebras immediately 

 below, and is called its tuberofity. Advancing far- 

 ther on this external furface, we obferve on moft of 

 the ribs another fmaller tubercle, into which liga- 

 ments connecting the ribs to each other, and to th~ 

 tranfverfe procefies of the vertebra, and portions of the 

 longifiimus dorfi, are inferted t Beyond this the ribs 



VOL. III. J make 



