This is called _gristle_ or _cartilage_.

You have, no doubt, seen the gristle on the end of a "soup-bone" or on one of the bones of a "joint of beef." ~15.~ The joint contains a fluid to oil it, so that the ends of the bones move upon each other very easily.

If the joints were dry, every movement of the body would be very difficult and painful.
~16.~ The bones are held together at the joints by means of strong bands called _ligaments_.
~17.

How the Bones are Made.~--The bones are not so solid as they seem to be.

The outside of most bones is much harder and firmer than the inside.