THE SKELETON 



ture, but that the bone is spongy near the ends, enlarged 

 for forming the joints. The cavities in this spongy por- 

 tion contain red marrow. A long bone is hollow, because 

 a given weight of material has more strength in the form 

 of a hollow cylinder than in the form of a solid rod. (Does 

 this imply that a hollow cylinder is as strong as a solid one 

 of the same size ?) 



118. THOUGHT LESSON. Classification of the Movable 

 Joints. The table below is to be filled out by the same 

 plan as in the Thought Lesson on page 68. 



119. Composition of Bone. Bone is covered with peri- 

 osteum. This is the name given to the close-clinging 

 fibrous covering of the bone, composed of connective tissue 



