236 A MANUAL OF DENTAL ANATOMY. 



And there are some fish, e.g., some of the large Siluroid 

 fishes, which have very strong, large teeth, an inch and a 

 half or more long, and very firmly anchylosed to the bone. 



It is not common for sexual differences to be met with 

 between the teeth of the male and female, though a slight 

 difference exists between the sexes in some species of Skate. 

 And although not strictly speaking a dental character, it 

 may not be out of place to mention here the peculiar 

 armature of the jaw of the male Salmon at the breeding 

 season. 



The end of the lower jaw becomes produced, and turned 

 upwards at its point; the stout cartilaginous hook thus 

 formed is of such dimensions that it has to be accommo- 

 dated in closure of the mouth in a deep cavity formed 

 for it between the intermaxillary bones. In some Canadian 

 salmon this process is supposed to be constant in the older 

 males, but in the British fish it disappears, and only exists 

 at the breeding season. A fish in which it is strongly 

 developed is a foul fish, and is called a Kelt. It is used 

 apparently as a battering ram, and such salmon are con- 

 stantly found killed, with their sides deeply gashed by the 

 charges of their opponents. 



Not much can be said in general terms of the structure 

 of the teeth of fish. The bulk of the teeth of most fishes 

 is made up of one or other modification of vasodentine or 

 osteodentine ; this is often glazed over upon its exterior by 

 a thin film of enamel, so thin as often to appear structure- 

 less. 



Unvascular dentine also forms the teeth of many fish, 

 and in some is remarkable for the fineness of its tubes ; in 

 fact, every form of dentine, from fine-tubed hard dentine 

 to tissue indistinguishable from coarse bone is to be found 

 in this class. 



Dentine of very complex structure (labyrintho-dentine) 

 is met with in some fish ; and an example from the Lepi- 



