108 SKELETON. 



of their cartilages joining the sternum, are called the sternal 

 or true ribs, and the lower five, from their cartilages stopping 

 short of the sternum, are called the false or asternal ribs. 

 Cases are recorded by several anatomists of there being eleven 

 or thirteen ribs on a side : the latter I have seen several times, 

 and the former but once or twice. In such cases, the dorsal 

 vertebrae correspond in number with the ribs. In the instances 

 of redundance which have come under my notice, the last rib 

 looked like a transverse process of unusual length, belonging to 

 a lumbar vertebra. The superabundant vertebra constituted 

 the thirteenth dorsal ; but was formed like the first lumbar as 

 it commonly exists, arid the last lumbar vertebra was entirely 

 anomalous in its shape, being intermediate in form to a lumbar 

 vertebra, and to the first bone of the sacrum. 



All of the ribs are so placed, that they run very obliquely 

 downwards and forwards from their posterior extremities. 

 This obliquity becomes the more striking as the ribs increase 

 successively in length. The first rib, for example, articulating 

 by its posterior extremity with the first vertebra of the back, 

 has its anterior extremity nearly on a horizontal line with the 

 lower part of the third dorsal vertebra. The seventh rib has 

 its anterior extremity on a horizontal line with the lower mar- 

 gin of the last dorsal vertebra, notwithstanding its posterior 

 extremity articulates with the seventh vertebra. The same 

 sort of comparison might be usefully instituted in regard to all 

 the ribs, in which case the rule will be found closely applicable, 

 with the slight exception of the two or three last ribs. The 

 ribs are nearly parallel to each other in this obliquity, allowance 

 being made for the effect which the obliquity of the sternum 

 has in causing a greater separation of their anterior extremities 

 from each other, than exists at their posterior extremities. 



Common points of resemblance between the Ribs. Each rib 

 is paraboloid ; presents an external and an internal surface ; an 

 upper and a lower margin; a sternal and a vertebral extre- 

 mity. 



The external surface of each rib is convex, while its internal 

 surface is concave. The former presents, not far from the ver- 

 tebral extremity, an oblique ridge, occasioned by the insertion 

 of the sacro-lumbalis muscle. It is precisely at this line that a 



