MOTION AND COORDINATION 



On the other hand, burning a bone destroys the animal 

 matter. When this is done the bone loses its toughness, 

 and becomes quite brittle. The prop- 

 erty of toughness is, therefore, sup- 

 plied by the animal matter. This 

 consists mainly of a substance called 

 ossein, which may be dissolved out of 

 the bones by boiling them. Sepa- 

 rated from the bones it is known as 

 gelatine. The blood vessels and 

 nerves in the bones, and the pro- 

 toplasm of the bone cells, are also 

 counted in with the animal matter. 



If a dry bone from a full-grown, but 

 not old, animal be weighed before and 

 after being burned, it is found to lose 

 about one third of its weight. From 

 this we may conclude that about one 

 third of the bone by weight is animal 

 matter and two thirds is mineral 

 matter. This proportion, however, 

 varies with age, the mineral matter 

 increasing with advance of years. 



Gross Structure of Bones. The 

 gross structure of the bones is best 

 learned by studying both dry and 

 fresh specimens. (See Practical 

 Work.) The ends of the bones are 

 capped by a layer of smooth, elastic 

 cartilage, while all the remaining sur- 



FIG. 93. -Section of faCG ls covered b Y a rather dense 

 a long bone (tibia), show- sheath of connective tissue, called the 

 ing the gross structure. periosteum. Usually the central part 



