46 THE STORY OF FISH LIFE. 



spines attained huge proportions. Thus the fin- 

 spine of an extinct shark, Oracanthus pustulosus, 

 from the carboniferous limestone of Bristol, was 

 three feet in length ! 



CHAPTER V. 



HEADS AND TAILS. 



The heads and tails of fishes, if looked at from 

 the right point of view, will force upon us still 

 further the truth of the story of evolution. 

 Moreover, the history of the making of these 

 very essential parts will serve us for object 

 lessons of patience, as exhibited by Dame 

 Nature ; very profitable for contemplation. The 

 old adage, "Rome was not built in a day," is 

 equally true of the fish. 



To get at the real inwardness, so to speak, of 

 the fish's head, we must start with an examina- 

 tion of this, as we find it in its most primitive 

 form. The dog-fish will serve us beautifully for 

 this purpose. 



If we remove the skin and muscles from the 

 head of a dog-fish we shall find, in the first place, 

 not bones, as some might have expected, but a 

 much softer material known as cartilage or 

 gristle. The skeleton of the dog-fish's head is, 

 therefore, not bony but cartilaginous. Further- 

 more, it is made up of several separate elements : 

 those which go to make the skull or cranium, 

 and those which constitute the upper and lower 



