44 ORAL EQUIPMENTS. 



most significant meaning to Evolutionists ; as birds 

 of recent times have no teeth. 



2. Attachment by " fibrous membrane," as attains 



amongst the Elasmobranchii, i.e., Sharks and Rays. 



3. " Ankilosis" or Bony union ; the typical method that 



attains in the Teleostei, and in Reptiles, i.e., such 

 fish as the Pike, Salmon, &c. 



There are many beautifully specialized modifications of 

 these type methods of attachment to serve the peculiar end 

 required, which I shall have to describe presently. 



These will, however, be better comprehended when the 

 typical methods have been fully understood. 



Attachment by " Gomphosis" has been sufficiently de- 

 scribed for our present purpose in my remarks on human 

 teeth and jaws. 



Taking the ordinary Skate or Ray, or Shark, we see an 

 excellent instance of the method of attachment by " Fibrous 

 union," and also are able to realise by the diagram before us 

 the way in which the teeth arise, develope, and come into 

 position. 



In this order of fish the oral epithelium to which the 

 teeth are attached are continuous with the skin of the back 

 and belly ; and is constantly, as the creature grows, sliding 

 over the lips, and what was once inside the mouth comes 

 outside. This peculiarity shows well the relationship between 

 the dermal spines and the teeth. 



As the skin slides outwards it carries along with it the 

 rows of sharp teeth which, as they come into place, become 

 erect and assume functional activity. As they wear down 

 they fall off and the skin slides outwards, while fresh rows 

 of teeth take their place. 



In cases where the teeth are attached by "Ankilosis" 

 there is almost always developed around it as it erupts a 

 special porous kind of bone — a bone of attachment — which 

 falls off or becomes absorbed when the tooth is lost. 



I have not a specimen to illustrate the order of coming 

 into place of teeth of this description ; but will try and illus- 

 trate it by the diagram. The Pike is a capital instance of 

 this method ; but it is also one of the creatures which pos- 

 sesses as well a special set of teeth adapted for pretensile 

 purposes. The plate in the book I show will give an idea 

 of the myriads of teeth this creature possesses. In fact, 

 every available spot on the inside of the mouth fairly 

 bristles with sharp teeth. 



The lower jaw is armed with a very formidable row of 



