ORAL EQUIPMENTS. 43 



cutting teeth, named central and lateral ; next come the 

 " canine," vulgarly called eye teeth ; then first and second 

 " hicuspides" or two cusped teeth, by Odontologists called 

 Premolars ; and lastly are the first, second and third molar or 

 grinding teeth ; the third molar being usually called the 

 " Dens bapientia" or wisdom tooth. This is the normal adult 

 complement, thirty-two in all. The deciduous or temporary, 

 or milk teeth as they are indiscriminately called, are only 

 twenty in number, there being no bicuspides, which grow in 

 the places of the temporary molars, and no wisdom teeth or 

 third molars. 



Each tooth consists of a crown, neck, and root or roots. 



Leaving minute particulars till the section dealing with 

 histological characters, I will now endeavour to explain 

 some of the interesting differences in the development, calci- 

 fication, growth and fixation of the teeth of the various 

 classes of animals. 



All teeth develop from a germ of soft materials, which 

 originates more or less deeply down in the jaw, becomes 

 calcified or hardened by a conversion of its substance into 

 the various tissues already alluded to, and gradually moving 

 nearer to the surface of the jaws takes its proper position in 

 the dental arch. We will now see how this takes place in 

 different classes of Cold-blooded Vertebrates. 



Amongst the Elasmobranchi, or Fishes with a cartila- 

 ginous skeleton, each tooth germ derives its origin from its 

 next oldest predecessor (we might almost compare it to the 

 growth of a plant from tubers). This method of succession 

 also attains amongst Reptiles. But amongst the Teleostei,,or 

 Fishes with an osseous or bony skeleton, each tooth germ 

 arises <( de novo," developed by a modification of the epithelium 

 of the jaw. 



Amongst all these classes there is an endless succession 

 of teeth. 



The various methods of attachment of teeth in Verte- 

 brates is very interesting. They are divisible under three 

 main heads : — 



1. Gomphosis, or implantation in a socket, more or less 

 complete. This is the typical Mammalian attach- 

 ment. There are a few examples amongst Fishes, 

 e. rj., the rostral teeth of the Saw-fish ; and also 

 amongst the Reptiles, e. g., Crocodiles and Alligators. 

 Certain extinct birds also had teeth implanted in 

 sockets. The fact of extinct birds having teeth at 

 all, much more teeth implanted in sockets, has a 



