ASYMMETRICAL CRANIA. 



29 



vided with radiating appendages wliicli give support to the 

 branchial mucous membrane. It is only found in those 

 Vertebrata which breathe by giUs — the classes Pisces and 



Fis. 10. 



Fig. 10. — The skull of a Plaice (Platessa vulgaris), viewed from above. 

 The dotted line a, b, is the true morphological median line ; Or. Or, 

 the position of the two eyes in their orbits; Eth, ethmoid; Prf, 

 prefrontal; Fr, left frontal; i^ri, right frontal ; Pa, parietal ; SO, 

 supra-occipital ; Ep. O, epiotic. 



A)wphibia. In the higher Vertebrata, the posterior of the two 

 pairs of comua with which the hyoidean apparatus is gene- 

 rally provided, are the only remains of the branchial skeleton. 



