90 THE RIBS. [chap. 



The sternal ribs are connected with the sternum either by 

 interposed fibrous tissue, or b}^ distinct synovial joints. The 

 first is attached to the side of the presternum, the second 

 opposite to the junction of the presternum and the first 

 mesosternal segment, and the succeeding ones opposite to 

 the interspaces between the other mesosternal segments ; 

 though two or more maybe attached to the hinder end of 

 the last of these segments. The inferior ends of the so- 

 called " false ribs " are attached by fibrous tissue, or by 

 synovial joints, to the hinder borders of the sternal ribs in 

 front ; though, as before said, the most posterior are free or 

 " floating." 



The ribs of Mammals never have " uncinate processes," 

 like those found in Birds and Reptiles. 



The most prevalent number is thirteen pairs ; the lowest 

 is nine (in Hypcroodon\ the highest twenty-four (in the Two- 

 toed Sloth, Chohepus. 



Special Characters of the Ribs in the various Groups of 

 Manunalia. Order Primates. — In Man there are nor- 

 mally twelve pairs of ribs, of which the first seven are 

 reckoned as true ribs, and the last two as floating ribs. 

 The last pair may be rudimentary or absent ; or, on 

 the other hand, the seventh cervical or the first lumbar 

 vertebra may have an additional movable rib articulated 

 with it. 



The first vertebral rib is much shorter, broader, flatter, 

 and more curved than the others. These gradually increase 

 in length until the seventh, after which they again diminish 

 to the twelfth. In breadth they gradually decrease from 

 tlie first to the last. 



The portion of the rib between the head and the tubercle 

 is called the neck ; it is wanting in the last two ribs, in 

 which the two attachments are blended. The greatest point 



