THE LEVERS OF THE BODY 



59 



A Lever 



Orders of 

 Levers. 



SUMMARY. 

 A rigid bar. 

 Movable round a fixed point (fulcrum). 



( One is called the power. 



If acted on by two forces -j The other is called the weight or 

 ( resistance. 



Crowbar. 

 See-saw. 

 Poker. 

 k The balance. 



1st Fulcrum belweeen power and weight- 



Levers of the 

 Body. 



2nd Weight between fulcrum and power \ 



3rd Pvwer between fulcrum dnd *%** {^^Ufa* f * ma ~ 



ist Onto Illustrated by I Sr C > in? f^f d on * tl ' 

 * ( Motion of body on the hip. 



2nd CWfcr-Illustrated by | Jr^g th u e kg ff *e ground. 

 ' i Raising the body on the toes. 



yd Or^r-Illustrated by \ ^^. the [ or f rm " 

 J > Extending the leg. 



QUESTIONS ON LESSON IX. 



1 . What is a lever ? Illustrate your answer by an example. 



2. Give common examples of the three orders of levers. 



3. Give an example of each of the three orders of levers as exemplified in 



the human body. 



4. Show how the three orders of levers may be illustrated by the foot. 



LESSON X. 

 THE CHEST AND ABDOMEN. 



THE student will remember that the body of a vertebrate animal 

 contains two distinct tubes or cavities. One of these is sur- 

 rounded by bony walls, and includes the cavity of the skull and 

 the spinal canal, which communicates with it. The other is the 

 great cavity which contains the organs of digestion, circulation, 

 &c. 



We will now proceed to notice the form of the great body cavity ; and 

 here we strongly recommend the dissection of a small animal. In this in- 

 stance an animal no larger than a rat will answer the purpose. Lay the dead 

 animal on its back, stretch out its limbs, and pin them firmly to a flat board. 

 Now take a sharp-pointed knife, and cut the skin from the throat in a straight 

 line down to the tail, taking care that the knife does not e-iter into thejtesh at 

 any point. Now loosen the skin from the flesh, and pin it also to the board, 

 spreading it out, right and left, to the greatest possible extent. The arrrange- 

 ment of the ribs may now be seen, with the thin walls of muscle or flesh 



