358 



THE MECHANICAL FUNCTIONS. 



junction, and at this angle a process occasionally 

 extends, for the purpose of forming connexions- 



with the neighbouring ribs. 



The ribs are connected in front with the breast 

 bone, or sternum (s), often by the intervention of 

 cartilages, which, from their similarity of form to 

 the ribs, appear as continuations of them, and 

 which complete the semicircle. These cartilages, 

 which have been termed sterno-costal appendices^ 

 often become ossified, either wholly or in part. 



The sternum has been considered as being formed 

 of nine elementary pieces, proceeding from sepa- 

 rate centres of ossification. Two of these occupy 

 the end which is nearest to the head ; four are 

 lateral ; and two are situated at the opposite ex- 

 tremity ; one only being central, and surrounded 

 by the rest. Speculative anatomists have laboured 

 to trace the developement of these several elemen- 

 tary parts in the different classes of animals, from 

 the rudimental states of this bone as it occurs in 

 Fishes, to its greatly expanded conditions in the 



