THE BONES. 11 



b. The articular extremities. 



1. How are these united to the shaft ? (See a bone 



that has been boiled until the extremities have 

 separated from the shaft.) 



2. The cartilage in the fresh bone. 



(1) How far does it extend? 



(2) What is its texture and color? 



3. The large prominences or knobs : their use ? 



c. Sketch and label all the external parts. 



II. THE INTERNAL PARTS. 



These may be seen from a longitudinal section of a fresh 

 bone of the leg of a sheep. 



a. The hard bone on the outside. 



1. Note the thickness in different parts of the bone. 



2. Where is it thickest ? Why ? 



3. Where is it thinnest? Why? 



b. The spongy bone in the ends. 



1. How far does it extend? 



2. What is its color in the fresh bone? That is 



due to the marrow within it. 



c. The fine cavities and passages : their use? 



d. The medullary cavity in the centre. 



1. What is its shape ? 



2. How far does it extend ? 



3. Which is stronger, a solid or a hollow shaft con- 



taining the same amount of material ? 



4. What, then, is the use of the medullary cavity? 



