VERTEBRATES 169 



7. How is flexibility of the column accomplished in 

 certain types or in certain places of one type ? How is 

 rigidity gained ? State instances in each answer. 



8. Examining the interior of the turtle's " shell," find 

 out and explain how the vertebrae have been modified to 

 form the upper " shell." How has the under portion 

 {plastron) been formed .'' 



9. In round numbers, which skeleton has the greatest 

 number of vertebrae and which the least .' 



10. Which skeleton has the greatest number of ribs, 

 and which has the least } 



11. In a summarizing statement explain any variations 

 you find in the pectoral and pelvic girdle for strength 

 (rigidity) ; flexibility. This answer may be written as a 

 table, naming the bones, opposite each stating its condition, 

 and then what it affords or is adapted to. 



•12. What is accomplished by having two bones in the 

 shank of the • leg .■' In what types or forms is there but 

 one, and which one is it .'' 



13. Can you assign any advantages in power, agility, 

 length of leg, or position of leg and foot accruing from a 

 long ankle ^ (See horse, frog, et al.) 



14. Enumerate the types or forms, and opposite each 

 state the number of fingers and toes. 



15. Make a table, heading one column " Form or type " ; 

 another, " Habitat " ; and a third, " Habit." Judging from 

 the structure which you see or from your previous knowl- 

 edge or experience, fill in the table, stating whether the 

 type is aquatic, terrestrial, or aerial ; whether it burrows, 

 walks, runs, or climbs, etc. 



16. From your statements in 15, explain how the 

 peculiar mode of life affects the structure of these types. 



