48 



THE HUMAN BODY. 



which dies if it be stripped 

 off.* The periosteum covers 

 the humerus except on its 

 ends (Cp, Tr, Cpl) at the 

 shoulder and elbow- joints ; 

 there the bone is covered by 

 a thin layer of gristle or car- 

 tilage. Very early in life the 

 whole humerus consists of 

 cartilage ; this is afterwards 

 absorbed and replaced by 

 bone, leaving only a thin 

 layer of articular cartilage 

 on each end. 



The bone itself consists 

 of a central nearly cylindrical 

 portion or shaft (extending 

 between the dotted lines X 

 and Z) and two articular ex- 

 tremities. These extremities 

 are enlarged to give a wider 



What are the functions of the 

 periosteum? Where is the perios 

 teum absent? Of what does the 

 humerus consist in very early in 

 life? What happens to most of its 

 cartilage afterwards ? Where is 

 some cartilage left? 



What are the main divisions of 

 the humerus? What is the general 

 form of its shaft? Why are its ar- 

 ticular extremities large? 



* Cases have been recorded in which a 

 considerable portion of a bone or even the 

 whole bone has been removed during life, 



AM *?&,= SMT.rft?&5 



tot. the oljj. 



