84 STUDIES OP ANIMAL LIFE. 



brane separating the chest cavity from the 

 abdominal cavity. 



2. How are the nostrils used in respiration? 



3. Is the mouth open in respiration ? 



4. What causes the air to flow into the mouth ? 



5. What forces the air into the lungs ? 



6. Why cannot a frog breathe as you do ? 



7. Does a frog breathe while under water ? (Place a 



frog in a deep jar of water.) 



8. Has the frog more than one method of respiration ? 

 Why must a frog keep its skin moist ? 



H. A Typical Muscle. 



For this study examine the large gastrocnemius muscle 

 of the shank, forming the " calf of the leg." (Use 

 a dead frog with the skin stripped from the leg.) 



1. What is the shape of this muscle ? 



2. Observe the tendon, a dense white portion at the end 



of the muscle by means of which it is attached to 

 the bone. 



3. Locate the points of attachment of the muscle to the 



bone. The proximal point of attachment is called 

 the origin of the muscle and the distal, the inser- 

 tion. 



4. What parts of the limb are moved b)' this muscle ? 



5. What is the advantage of tendon ? 



6. Is the gastrocnemius a fiexor or an extensor muscle ? 



7. Where is its opposing muscle ? Why is this smaller ? 



8. Draw an outline of the leg to show the gastrocnemius 



with its opposing muscle and also their relation to 

 the leg and foot. 



I. The liiver and Heart. (Dem.) 



The liver as seen from a ventral view is a large, dark- 



