SCALES 



231 



There are no true fulcra in any Dipnoi. The head and shoulder 

 of Dipterus are provided with plates of a structure similar to that 



B. 



A. 



,s. 



Fio. 200. 



A, scale of Ccratodns Forstcri, Krcfft. B, enlarged view of a portion of the outer surface of 

 the scale of Protopteriis annectens, Owen, a, anterior edge ; I, front limit of exposed region of 

 scale ; j>, posterior edge ; s, spine ; t, layer of bone-like tissue. 



of the scales. The lateral-line canals are embedded in these plates 

 and scales in the early forms. 



A minute comparison of the exoskeleton of the fossil and living 

 Dipnoi yet remains to be made. In the more modified forms the 



Fio. 201. 



Enlarged view of a small portion of the scale of Phanerojrtntron curtum, Wht. ; Upper 

 Devonian, Canada, i, inner bony layer ; sp, surface spinelet ; re, vascular space. 



ganoid surface disappears from the plates, leaving only sheets of 

 bone, sunk far below the surface in living genera. The scales also 

 lose their cosmine layer, which appears to be represented by numerous 



