CHAPTER III 



THE SKELETON 



Experiment i. (At home.) Is the Arch of the Foot Elastic? 

 Wet the foot in a basin of water and, while sitting, place the foot flat 

 upon a piece of paper. Draw the outline of the track. Repeat, but 

 stand with your whole weight upon the foot. Draw track. Con- 

 clusion? (Take sketches to school. Which sketch shows the flattest 

 foot?) Devise a method for measuring the length of the foot with 

 and without the weight of the body upon it. What difference? Con- 

 clusion ? 



Experiment 2. Composition of Bone. Place a bone in a hot fire and 

 let it remain for three or four hours. It will keep its shape however long 

 you burn it ; but unless you handle it carefully when you take it out, it 

 will crumble to pieces. If not thoroughly burned, the bone will be 

 black from the carbon of the animal matter still left in it. Experiment 3. 

 Obtain a slender bone like the rib of a hog or the leg bone of a fowl, 

 and put the raw bone into a vessel containing strong vinegar or two 

 ounces of muriatic acid and a pint of water. Leave it there for four 

 days. When the bone is taken out, it can be tied into a knot. The 

 acid may be washed off, and the bone preserved in a bottle of alcohol 

 or glycerine. 



Experiment 4. The Forms of Joints. Obtain the disjointed bones 

 of a fowl or small mammal and place them one at a time in their 

 sockets and study the fit and motion of the joints. 



Experiment 5. Pivot Joints. Through what fraction of a circle do 

 the pivot joints in the forearm and neck allow the hand and head to 

 rotate ? 



Review Questions. Where are the bone cells? How does nour- 

 ishment reach them? How has the mineral part of the bones been de- 

 posited? How long may bone cells live? Name animals with outside 

 skeletons. Inside skeletons. No skeleton. 



Forms and Uses of Bones. The three chief uses of bones 

 are protection, motion, and support. In order to fulfill 

 these purposes, the bones must have different sizes, shapes, 



and positions. The bones are classed by shape, as long, 



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