ORAL EQUIPMENTS. 45 



teeth. The margin of the upper maxilla? has more, and there 

 are but a few small ones on the premaxillse ; but there are 

 three broad bands on the palate, the medium (on the vomer) 

 looking backwards, and the two lateral (on the palate bones) 

 looking backwards and inwards. On the tongue, the bron- 

 chial bones, and in fact covering the whole throat are teeth. 

 Woe betide the poor wretch of a perch or roach which is 

 once seized by this formidable enemy ; or a man who gets his 

 finger caught. 



The teeth on the three bands on the palate are attached 

 in a very special way. It is called the " watch-spring hinge" 

 method. I will endeavour to draw it on the black-board. 



The mackerel has also hinge teeth, but they do not 

 spring into place of themselves, but lie down flat, pointing 

 backwards, but are stopped from bending forwards by a 

 buttress of bone. 



The specimen of a " Sargus" or " Sheep's-head Fish" jaws 

 I pass round will well illustrate another example of differenti- 

 ation of organs to meet the requirements of a creature's 

 environments. 



A brief reference to the teeth of the " Pristis" or " Saw 

 Fish" must close my remarks on Fishes, as a still more inte- 

 resting family, the Reptiles, awaits our attention. 



The oral equipment of the Pristis is the same as others of 

 the shark and ray order : but the teeth which are fixed to the 

 rostrum or snout, which give it its name of " Saw Fish," are 

 very peculiar. They are socketed and attached by " gomp- 

 hosis." A very rare feature in the attachment of the teeth of 

 cold-blooded vertebrates. Moreover they grow from persistent 

 pulps ; another rare occurrence amongst that class. 



REPTILIA. 



Remembering at the outset that the teeth of reptiles are 

 for the most part attached by ankylosis, and succeed one 

 another from beneath, it will be interesting to notice a few of 

 the most notable departures from this rule. 



Starting with the most familiar the " Batrachia," we find 

 that toads are edentulous, being endowed with hard plates of 

 bone round the margin of the jaws, which serve the same 

 purpose. Frogs have no teeth in the lower jaw, and only one 

 row in the upper jaw, which are on the maxillary bones and a 

 few on the vomer ; and their method of attachment, growth, 

 and development follows the rule sufficiently closely, as 

 to warrant our passing them over in a paper like the 

 present. 



