The Skull Die 
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 
Fic. 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 
