PLATE 3 



EXPLANATION OF FIGURES 



13 Transverse section of the neural arch of the vertebra of a normal control 



tadpole killed before metamorphosis, total length 52 mm., body length 23 mm. 

 The legs have reached a length of only 12 millimeters. This shows the amount 

 of endochondral ossification present. 



14 Transverse section of the neural arch of the vertebra of a thyroidless 

 tadpole killed October 14, total length 80 mm., body length 29 mm. showing the 

 amount of endochondral ossification present. 



15 Cross section through the neural arch of the vertebra of a normal control 

 frog killed two months after metamorphosis, showing the periosteal bone and 

 osteogenic tissue. 



16 Cross section through the neural arch of the vertebra of a thyroidless 

 tadpole killed December 15, total length 52 mm., body length 23 mm. showing 

 the periosteal bone formation and the endochondral ossification. 



17 Surface view of a four and one half millimeter hind leg of a thyroidless 

 tadpole killed October 14, total length 80 mm., body length 29 mm. showing the 

 cartilage and bone formation. 



18 Surface view of a 12 mm. hind leg of a normal control tadpole total length 

 52 mm., body length 23 mm. showing the cartilage and bone formation. 



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