Bones of the Thorax. 79 



Facies articularis 

 capituli costae 



i Collum costae 



Crista capituli _.t" * JK^ >. Crista colli costae 



Capitulum costae 

 Tuberculum costae 



Angulus costae 



98. Eighth rib of right side, costa Mill, from behind. 



The middle piece or shaft of the rib, corpus costae, forms lateralward from the tuber- 

 culuni costae an angle which is directed backward and downward, the angulus costae. This 

 lies on the first rib close to the tubercle ; on succeeding ribs it is situated ever more lateral- 

 ward; it is most marked on the middle ribs and is absent from the last two ribs. The body 

 of the rib is a flat plate of bone with an internal and an external smooth surface ; the external 

 surface is directed vertically in the middle ribs, markedly upward in the uppermost ribs, more 

 downward in the lowermost (see Figs. 105 107). The curvature of a whole rib is double, 

 since in the first place the surface of the shaft is bent so as to be convex lateralward and 

 in the second place, its upper edge is curved so as to be concave or CO -shaped. On the internal 

 surface near the lower margin runs the sulcus costae (for the v., a. and n. intercostalis) ; it begins 

 at the tubercle, is most marked behind and becomes lost in front; on the first and last ribs 

 it is absent or only slightly indicated. The anterior extremity is less broadened and ends in 

 a rough depressed surface for the reception of the costal cartilage. 



The cartilage costalis (costal cartilage) (see Fig. 105) has in general the same 

 shape as the rib. It unites in front with the sternum or is attached to the cartilage of the 

 next rib above. The cartilages increase in length from the first to the seventh ; from this on 

 they decrease so that the cartilage of the eleventh and twelfth ribs are only short pointed 

 pieces. The first two costal cartilages only follow the same direction as the bony parts of their 

 ribs, the others are more or less curved upward at their anterior extremities. The costal 

 cartilages often become calcified in old age, the first most frequently. 



