THE STERNUM. 



461 



dian line at the front part of the thorax. Its direction IB 

 obliquely downward and forward, its superior end being 

 consequently nearer the spine than the inferior. Its upper 

 portion is on a A FIG. 137. 



level with the 

 third dorsal, 

 and its lower 

 with the elev- 

 enth dorsal ver- 

 tebra. Its ave- 

 rage length is 

 six inches. 



The sternum, 

 in the adult, 

 consists of three 

 pieces a supe- 

 rior, middle, and 

 inferior, which, 

 in old age, are 

 often fused into one. The superior lone is quadrilateral in 

 shape, thick and broad above, narrow below, and concave 

 transversely at its upper edge. The interclavicular liga- 

 ment occupies this concavity, at either end of which, corre- 

 sponding to the angles, are the articular cavities for the 

 sternal ends of the clavicle. Just below this articulation 

 is a depression on each side for the cartilage of the first rib, 

 and still lower down, at the point of junction with the 

 second piece, there is, on each side, a half fossa, which, with 

 a similar one upon the second bone, receives the cartilage 

 of the second rib. The middle lone is much longer than 



Fia. 137, A represents a front view of the Chest, a First bone of the ster- 

 num. 6 Second bone of sternum, c Third bone of sternum, called ensiform 

 cartilage, d First dorsal vertebra, e Twelfth dorsal vertebras. /First rib. 

 g Head of first rib. h Neck, t Tubercle, j Seventh or last true rib. k k Cos- 

 tal cartilages. I Floating ribs, m Groove for the intercostal artery. 



FIG. 137, B represents the Sternum, a First piece. 6 Second piece, c 

 Third piece, or ensiform cartilage, d Articular face for clavicle, e Articu- 

 lar surface for first rib. / Articular surface for second rib. g h i j Articular 

 urfaces for the last five true ribs. 



