THE SKELETON 



17 



All these bones are fastened together by ligaments, or 

 by cartilages ; and where they play freely over one 

 another, a coat of cartilage furnishes the surfaces which 

 come into contact. The cartilages which thus form part 

 of a joint are called articular cartilages, and their free 

 surfaces, by which tliey rub against each other, are lined 

 by a delicate synovial membrane, which secretes a lubri- 

 cating Huid — the synovia. 



Fifi. 4.— The Pelvis. 



Sac. sacrum ; Cocc. coccyx; il, <s>, pu, ilium, ischium, pubis, three parts 

 of the innominate or hip bone ; acct, acetabuhini cup for head of femur ; 

 5 L. V, &th lumbar vertebra. 



5. The Erect Position. — Though tlie bones of the skele- 

 ton are all strongly enough connected togetherby ligaments 

 and cartilages, the joints play so freely, and the centre of 

 gravity of the body, when erect, is so high up, that it is im- 

 possible to make a skeleton or a dead body support itself 

 in the upright position. That position, easyasitseems, is the 

 result of the contraction of a multitude of muscles which 



C 



