The Skull 



113 



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.— C.ill-hars of Shark. 



of this group — Elasmohranchs, or strap-gilled fishes. 

 There are usuall}' five of these gills, and within each 

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



All this may be very true, sa}^ 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 



