218 THE BIOLOGY OF THE ANIMAL 



the maaner in which the radio-ulna articulates 

 with the humerus. Note the olecranon process 

 back of the elbow-joint. In how many directions 

 may the forearm be moved ? Compare with the 

 humerus and with your own forearm. Draw the 

 bone. 



Study the bones in the wrist, using a lens if 

 necessary. How many carpal bones are there? 

 How are they arranged ? Of how many motions 

 is the frog's wrist capable ? Compare with those 

 of your own wrist. How do you account for the 

 differences ? What is the natural position of the 

 hand of a living frog? How many digits do you 

 find in the skeleton of the hand ? Compare with 

 the number visible in the hand of the living frog. 

 Examine the first bone or metacarpal in one of 

 the digits. "What is its shape ? Compare all of 

 the metacarpals. What differences do you notice? 

 Notice that, in addition to the metacarpal, each 

 digit consists of a number of smaller bones, the 

 phalanges. How many do you find in each 

 digit ? What variations in shape and size of the 

 phalanges in a single digit ? Does the thumb or 

 pollex differ in structure from the other digits ? 

 Of what motions are the digits capable? Draw 

 the frog's hand. Compare the structure of the 

 frog's hand with your own. What important 

 skeletal differences can you distinguish ? 



e. The pelvic girdle. — What is its shape? In which 

 direction does it extend ? Is it attached to the 

 axial skeleton more or less firmlj^ than the pecto- 

 ral girdle ? What is its relation to the urostyle ? 

 Examine the left half, and endeavor to make out 



