The Skull 1 1 3 



it brings vividly to mind the image of an animal which 

 must have once existed a fish-like creature with no 

 jaws, but with a gristly mass which held up and pro- 

 tected the delicate blood-fringes, or gills, by means of 

 which all true fishes breathe. 



Our shark is a very convenient starting-point, and 

 before going further we should mention the technical name 



FIG. 87. Gill-bars of Shark. 



of this group Elasmobranchs, or strap-gilled fishes. 

 There are usually five of these gills, and within each 

 strap or fold of skin is a jointed arch of gristle. 



All this may be very true, say you, but what bearing 

 has it on the skull of the chicken? 



We have seen that in sharks the number of gills has 

 been greatly reduced, and a pair of very loosely attached 

 jaws has been acquired, and the truth gradually dawns 



