6 CHARLES S. TOMES. 



ment of the hinge ; in its complete condition it consists of 

 many well-defined, wavy bands of fibrous tissue, continuous 

 at one end with processes of bone, at the other with pro- 

 cesses of osteo-dentiue (see fig. 5). Like the far finer bands, 

 which have already been described as conferring upon the 

 tooth its resiliency, they appear to be continuations of 

 the calcifying rods of osteo-dentine, in which calcifica- 

 tion has stopped short and has left them soft ; they distinctly 

 belong to the dentine, and are derived from its formative 

 tissues, and not from any portion of the dental sac, as was 

 supposed to be the case with the hinges of the teeth of 

 Lophius. 



Attention has already been drawn to the fact that hinged 

 teeth have been found in three fish so dissimilar as to pre- 

 clude any idea of near genetic relationship, i.e. the angler, the 

 hake, and the pike ; but while the same mechanical result 

 is arrived at the means are slightly diff'erent. In the case of 

 the angler and the hake the elasticity resides solely in the 

 tissue of the hinge, so that, everything else being severed, 

 the tooth is as resilient as ever ; in the pike the hinge is not 

 in the least endowed with elasticity, but the bundles of fibres 

 proceeding from the interior of the dentine cap are exceed- 

 ingly elastic. 



Again, the tooth of the hake is furnished with a living 

 pulp, richly vascular, the vessels of which enter through the 

 hinge so as not to be put upon the stretch by the movement 

 of the tooth, while the hinged tooth of the pike is a compara- 

 tively pulpless structure. 



Of this incompleteness of the communication I am very 

 fully aware ; but as it may be long before I am able to enter 

 more thoroughly into the study of these particular structures 

 it has seemed better to offer these observations, imperfect as 

 they are, than to withhold all notice of an adaptive modifica- 

 tion which appears to me peculiarly suggestive. 



