402 



THE MECHANICAL FUNCTIONS. 



which they are composed, often form an angle 

 by their junction, and at this angle a process 



Q 



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 inter- 

 vention of cartilages, which, from their simi- 

 larity of form to the ribs, appear as continuations 

 of them, and are provided apparently to eke out 

 the remainder of the semicircle. These carti- 

 lages, which have been termed the sterna-costal 

 appendices, often become ossified, either wholly 

 or in part. 



The sternum is formed of nine elementary 

 pieces, each proceeding from a separate centre 

 of ossification. Two of these occupy the end 

 which is nearest to the head, four are lateral, 

 and two are situated at the opposite extremity : 



