CABTILAGES OP THE BIBS. 465 



The second rib in some measure resembles the first in hav- 

 ing little or no angle or twisting, and partly presenting 

 upward. The tenth rib has but a single articular surface. 

 The eleventh and twelfth have likewise but one articular 

 face, have no neck, angle nor tuberosity, and are pointed at 

 their extremity. 



The ribs are spongy, with a thin covering of compact 

 matter. Their development is from three points of ossifica- 

 tion one for the body, one for the head, and one for the 

 tuberosity. Ossification begins in the body of the rib 

 sooner than in the vertebras. In the epiphysis it begins 

 between the sixteenth and twentieth years ; and complete 

 union of all the parts takes place about the twenty-fifth 

 year. Each rib articulates by its head, with two contigu- 

 ous vertebra3, except the first and the last, which articulate 

 each with a single vertebra ; each unites also, by its ster- 

 nal end, with the costal cartilage. 



Cartilages of the Ribs. The costal cartilages are of the 

 permanent class, and are regarded as part of the skeleton 

 of the chest. They are situated at the anterior extremities 

 of the ribs, the seven uppermost of which they connect 

 with the sternum. The first is short the rest increase 

 successively in length, to the seventh ; and from this to the 

 last they diminish, so that the twelfth has merely a tip of 

 cartilage. The costal extremity of each cartilage is broader 

 than the sternal. The depression in the end of the rib 

 receives the former, while the cavities along the sides of 

 the sternum, receive the latter. Their anterior surface is 

 convex, and gives origin to the great pectoral muscle. The 

 posterior is concave and lined partly by the pleura. Their 

 margins, like the ribs, bound the intercostal spaces, and 

 give attachment to the internal intercostals. The first cos- 

 tal cartilage is short, broad, and descends obliquely down- 

 ward in the direction of the first rib; the second and third 

 are nearly horizontal; the rest ascend more and more. The 

 three superior cartilages of the false ribs are blended the 

 one with the other, and the two lower, as already stated, 

 are free and floating. 

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