THE RIBS. 



463 



The ensiform cartilage does not join the sternum till late 

 in life, about forty or fifty years. It articulates with sixteen 

 bones, the two clavicles and seven true ribs on each side. 



THE KIBS, (COSm) 



The ribs are twenty-four in number, twelve on each side, 

 and are divided into the true and false. The true are seven 

 in number, extend from the vertebra? to the sternum, and 

 are called vertebro-sternal. The false extend from the ver- 

 tebras to the ribs, and are called the vertebro-costal or aster- 

 nal. The two last having their extremities free, are called 

 FIG. 138. floating ribs, 



and are the 

 shortest. The 

 ribs present an 

 arched form, 

 and run ob- 

 liquely down- 

 ward and for- 

 ward from the 



vertebrae towards the sternum. They increase successively 

 in length from the first to the eighth, and then diminish to 

 the last. The breadth diminishes gradually from the first 

 to the twelfth. 



Common characters of the Eibs. Each rib consists of two 

 extremities, a vertebral and sternal, two surfaces, external 

 and internal, and two margins, superior and inferior. The 

 vertebral extremity or posterior end has a head, neck, and 

 tubercle. The head is divided by a middle ridge into two 

 articular faces, which are received into corresponding pits 

 on two contiguous vertebrae, the edge between them sinking 

 into the intervertebral substance. To the ridge the inter- 

 articular ligament is attached. The neck is the contracted, 

 round, and thick portion upon which the head rests. It is 

 situated before the transverse process, to which it is attached 

 f ,.-, 



FIG. 138, A represents the upper surface, B the lower surface of a rib. 

 Head of rib. & Tubercle, c Anterior end for costal cartilage, d Groove 

 for artery and nerve, e Angle of rib. 



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