220 THE BIOLOGY OF THE ANIMAL 



bones and the phalanges with the correspond- 

 ing parts of the fore limb. Look for other nu- 

 tritive foramina in the different bones of the 

 hind limb. 



What resemblances and differences can you 

 trace between the arrangement and structure of 

 the frog's skeleton and that of the lobster ? Be- 

 tween the motions allowed by the joints ? Com- 

 pare the frog's with a human skeleton or with 

 pictures of the same. Does the frog have a pa- 

 tella or " knee-cap " ? Is there a corresponding 

 bone at the elbow ? 



B.-^The Muscular System. 



Examine the muscles of an alcoholic specimen 

 in a pan containing fifty per cent, alcohol. Keep 

 the specimen moist all the time. Remove the 

 skin from the entire body, noting the threads 

 and bands of connective tissue which bind the 

 skin to the underlying parts. In what regions is 

 the skin loosely attached? At what points is it 

 most closely fastened ? Can you give any reasons 

 for this arrangement of the skin? Wash away 

 any coagulated substance, the Ijmipli, which may 

 be found lying in the depressions between the 

 muscles, and trim away the ragged ends of con- 

 nective tissue. Note the groups of muscles in 

 the various regions. What distinctions can you 

 give between those of the abdomen and those of 

 the limbs? What is the color of the muscles? 

 Are any of them so thin as to be almost trans- 

 parent ? If so, where are they ? How do you 

 distinguish one muscle from another ? In study- 

 ing each muscle, separate it carefully from its 



