O SITUATION. ATTACHMENT. 



present examples of teeth developed in the median hne of the mouth, 

 as in the palate of the myxines, or crossing the symphysis of the 

 lower jaw, as in the scymnus and myliobates. 



5. Attachment. — The teeth of fishes present greater diversity in their 

 mode, as well as place of attachment, than is observable in those of any 

 other class of animals. In a few instances, they are implanted in sock- 

 ets, to which they are attached only by the surrounding soft parts, as 

 e. g., the rostral teeth of the saw-fish. (1) Some have their hollow base 

 supported, like the claws of the feline tribe, upon bony prominences, 

 which rise from the base of the socket ; the incisors of the file-fish 

 afford this curious example of a double gompliosis, the jaw and the 

 tooth reciprocally receiving and being received by each other. (2) 



Theteeth of the Sphyrwna, Acanthurus, Dictyodus, &c., are examples 

 of the ordinary implantation in sockets, with the addition of a slight 

 anchylosis of the base of the fully-formed tooth with the parietes of the 

 alveolar cavity. But by far the most common mode of attachment of the 

 fully-formed teeth in the present class, is by a continuous ossification 

 between the dental pulp and the jaw ; the transition being gradual 

 from the structure of the tooth to that of the bone : the tooth, 

 prior to the completion of the anchylosis, is connected by ligamentous 

 substance, either to a plain surface, an eminence, or a shallow depres- 

 sion in the jaw-bone. 



Sometimes not the end, but one side of the base of the tooth is 

 attached by anchylosis to the alveolar border of the jaw ; it might be 

 supposed that, in this case, the crown of the teeth in both jaws 

 w^culd project forwards instead of being opposed to one another, 

 and such, in fact, must have been their position w^ere it not that, in 

 some instances, as in the Pimelipterus, the teeth have the crown 

 bent down at nearly a right angle with the base. In the scarus, 

 and likewise in the marginal teeth of the diodon, wdiere the teeth 

 are straight, and attached horizontally to the margin of the jaws, 

 their sides instead of their crowns are actually opposed to one another . 



In the cod-fish, wolf-fish, and some other species, m proportion 

 as the ossification of the tooth advances towards its base and 

 along the connecting ligamentous substance, the subjacent portion 

 of the jaw-bone receives a stimulus, and developes a process corres- 



CO PI. 8, fig. 3. (2) PL 40, figs. 3 and 5, a. 



