VON baer's principle. 99 



12. What is the difference between the fore and the 



hind legs? 



13. How many toes on each foot? 



14. What are the parts of the fore leg? Of the hind 



leg? 



15. Is there a diaphragm? 



16. Are there any ribs? 



17. How does a frog breathe? 



18. What organs in the body cavity? 



19. What shape is the stomach? 



20. How many lobes has the liver? 



21. Is there a bile sac? 



22. Is there a cloaca? 



23. What tube leads air into the lungs? 



24. Where is the larynx? 



25. What is the size of the lung cells? 



26. How many chambers has the heart? 



27. Describe the aorta. 



28. What branches does the aorta give off? 



29. What veins bring blood back to the heart? 



30. How many vense cavae? 



31. What veins unite to form each? 



32. Name all the parts of the brain. 



33. What nerves did you see? 



34. How many spinal nerves ? 



35. How many roots has each nerve? 



36. How many vertebrae? 



37. Name the bones of the pelvic girdle. 



38. Name the bones of the shoulder girdle. 



39. How many condyles? 



40. Where is the mylohyoid muscle? 



41. What are the breathing organs of a tadpole? 



Von Baer's Principle. 



When the frog eggs are first laid, each consists of 

 a single cell. Under proper conditions, the egg cell 



