SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 203 



263. THE SKELETON is DIVISIBLE on the middle line 

 of the Body into two similar halves, or two wholes, as a 

 person prefers to speak of it, most of the bones in each 

 being complete and undoubtedly double, as the ribs, 

 aim-bones, etc., and others being seen as double only 

 when observed with a philosophical eye, as the vertebrae. 



264. THE BONES ARE CLASSED as long, tabular or 

 broad, irregular, and short ; examples of which will be 

 recognized by an observation of the illustrations in the 

 plates. 



265. THE BONES ARE CONSTRUCTED with very un- 

 even surfaces, and with many projecting points, called 

 processes, to allow surface for the attachment of tendons 

 and ligaments, and also to give the muscles a leverage 

 power. 



266. THE HARDNESS OF THE BONES not only in- 

 creases with the age of a person, but it differs in differ- 

 ent bones at the same age, and indeed in different parts 

 of the same bone. 



267. THE GRISTLE OR CARTILAGE differs in its form, 

 thickness, and elasticity, at different joints. In some 

 parts of the body it gradually changes to bone, as in the 

 case of the lower extremity of the breast-bone or sternum, 

 and the cartilages of the ribs ; while in other cases it 

 never ossifies, as changing to bone is termed. 



268. Remark. It is easy to determine if a fowl is young, by ob- 

 serving if the point of the breast-bone yields. 



269. THE GRISTLE THAT COVERS THE ENDS OF BONES 

 IN FORMING JOINTS is thicker in the centre than at the 

 sides of the ball, and thicker at the sides than at the 

 centre of the socket. 



270. THE FORMS OF THE JOINTS are various. In 

 some cases, as in the skull, the bones are locked together 

 immovably; in other cases, as those of the thigh and 

 shoulder ball-and-socket joint, there is a very extensive 



26: 1 . How? 264. How ? 265. How? 266 Whnt. said -? 267 What 

 said ? 268. What said of fowl ? 269. What said - ? 270. What said ? 



