80 



§ 82. The ribs of the higher animals are, Hke 

 like those of the snake, attached to the spine by 

 ball and socket joints. The relative positions of 

 the ball and socket, however, are reversed, the 

 rib now carrying the ball; and tivo vertebrae, at 

 the sides of their junctions, carrying the socket. 

 Also, the further extremities of the ribs, which in 

 the snake would have been their " ground-ends,'* 

 are elastically joined on either side to a solid 

 piece of bone called the hreast-hone, or " sternunL' 



This bone, which represents all the ligamentous^ 

 scutae of the snake (§§ 44, 66) consolidated, may 

 be considered as a substitute ground on which the 

 ribs perform their movements, as those of the 

 snake do on the real ground. At each spring the 

 breast-bone is taken up and carried to the position 

 required for the next effort. 



Almost the whole length of this artificial ground 

 is occupied, on both its sides, by the attachment 

 of only part of the ribs, namely, of the first divis- 

 ion from the head, called the " true ribs." These 

 are separately articulated to it — each rib by the 

 end of its elastic prolongation. 



Of the remaining division, called the "false 

 ribs,'' each rib has a longer and still more elastic 

 prolongation than a true rib ; but these prolonga- 



