xvi INTRODUCTION. 



not undergoing that rapid spontaneous decomposition, after the 

 departure of hfe, to which other parts of the body are subject, 

 but enduring for ages without losing even its original shape. 



During the earlier periods of fcetal existence, we find no bone 

 whatever in the body — nothing but pieces of gristle or cartilage^ 

 assuming the forms of the bones into which they become at 

 various periods afterwards converted : cartilage being a firm, 

 solid, flexible substance, intermediate in its degree of hardness 

 between bone and flesh, and serving many useful purposes in the 

 animal economy, for which bone would be too stiff, unyielding, 

 and brittle, and other material too soft and unsubstantial. For 

 this reason it is employed in the temporary place of bone, in the 

 foetus ; and for the same reason, in some parts — in the ears, nose, 

 windpipe, &c. — is continued as a substitute for it during life. 



No less than two hundred and thirty-eight bones are found to 

 be required to complete the fabric of the skeleton ; which (in 

 order for them to admit of elasticity and motion) are linked and 

 joined one to another by curious, highly ingenious methods of 

 connexion, that come, indiscriminately, under the general deno- 

 mination of joints. Such, however, is the variety observable 

 among the joints, that anatomists have found it necessary to make 

 some sort of classification of them. The most natural and con- 

 venient one seems to be that which arranges them in three 

 classes : — Fii'st, into membranous joints, formed for elasticity 

 only, such as those of the cranium and face. Secondii/, into 

 cartilago-ligamentous joints, designed both for elasticity and 

 motion ; such as the connexion existing between the splint and 

 cannon bones ; between the bones of the pelvis ; and between 

 the vertebree of the spine, and the ribs and the breast-bone. 

 Lastly, into capsular joints, the most perfect but the most com- 

 plicated description of articulation, and the one intended solely 

 for the purpose of motion, simple or compound, according as the 

 necessities of the parts themselves may require. In the con- 

 struction of this kind of joint we find, first, the ends of the 

 bones forming it to be nicely shaped and fitted to each other ; 

 secondly, the adjusted extremities of the bones to be covered 

 with cartilage, to render them smooth and polished like ivory ; 

 thirdly, a capsule of a membranous nature attached around and 



