876 



TEETH. 



their sides instead of their summits (Scams*); 

 in Pimelodus, however, where the teeth are 

 thus attached, the crown is bent down in 

 the upper teeth, and bent up in the lower 

 ones, at right angles to the fang, so that they 

 oppose each other by the normal surfaces. 

 Certain teeth of recent and fossil cartilagi- 

 nous fishes have their base divided into 

 processes like fangs, but these serve for the 

 attachment of ligaments, and are not set in 

 bony sockets like the true fangs or roots of 

 the teeth of the Mammalia. Some Sharks 

 have two divaricating fangs ; some fossil teeth 

 referred to my genus Pctalodus by Agassiz, 

 with the specific name " radicans" have the 

 base divided into several fangs or processes, 

 indicating a generic distinction. The base 

 of anchylosed teeth is, at first, attached to 

 the jaw-bone by ligament ; and in the Cod- 

 fish, Wolf-fish, and some other species, as 

 calcification of the tooth progresses towards 

 its base, the subjacent portion of the jaw- 

 bone receives a stimulus, and developes a 

 process corresponding in size and form with 

 the base of the tooth : for some time a thin 

 layer of ligamentous substance intervenes, but 

 anchylosis usually takes place to a greater or 

 less extent before the tooth is shed. Most of 

 the teeth of the Lophius retain the primitive 

 ligamentous connection ; the ligaments -j- of 

 the large internal or posterior teeth of the 

 upper and lower jaws, radiate on the corre- 

 sponding sides of the bone, the base of the 

 tooth resting on a conformable alveolar pro- 

 cess. The ligaments do not permit the tooth 

 to be bent outwards beyond the vertical posi- 

 tion, but yield to pressure in the contrary direc- 

 tion, by which the point of the tooth may be 

 directed towards the back of the mouth ; the 

 instant, however, that the pressure is remitted, 

 the tooth returns through the elasticity of 

 the bent ligaments, as by the action of a spring, 

 into its usual erect positions (fig. 512, c. c. 

 Vol. III. p. 978. art. PISCES) ; the deglutition 

 of the prey of this voracious fish is thus facili- 

 tated, and its escape prevented.^ The broad 

 and generally bifurcate bony base of the teeth 

 of Sharks is attached by ligament to the semi- 

 ossified crust of the cartilaginous jaws ; 

 but they have no power of erecting or de- 

 pressing the teeth at will. The small and 

 closely crowded teeth of Kays are also con- 

 nected by ligaments to the subjacent maxillary 

 and mandibnlar membranes. The broad tes- 

 selated teeth of the Myitobatcs have their 

 attached surface longitudinally grooved to 

 afford them better hold-fast, and the sides of 

 the contiguous teeth are articulated together 

 by serrated or finely undulating sutures, a 

 structure unique in dental organisation. || The 

 teeth of the Sphyrcena 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 alveolar pa- 



* Odontography, pi. 49 ; and art. PISCES, Vol. III. 

 fig. 516, p. 979. 



t See art, PISCES, Vol. III., fig. 512 d, p. 978. 

 j Odontography, p. 154. 

 Art. PISCES, Vol. III., fig. 510, p. 97G. 

 || Odontography, p. 40. pi. 27 c. 



rietes ; and the compressed rostral teeth of 

 the Saw-fish are deeply implanted in sockets. 

 In the latter the hind margin of their base is 

 grooved, and a corresponding ridge from the 

 back part of the socket fits into the groove, and 

 gives additional fixation to the tooth. Some 

 implanted teeth in the present class have their 

 hollow base further supported, like the claws 

 of the feline tribe, upon a bony process aris- 

 ing from the base of the socket ; the incisors 

 of the Balistes, e.g., afford an example of this 

 double or reciprocal gomphosis. In fact, the 

 whole of this part of the organisation of fishes 

 is replete with beautiful instances of design, 

 and instructive illustrations of animal me- 

 chanics. The vertical section of a pharyngeal 

 jaw and teeth of the Wrasse (Labrus *) would 

 afford the architect a model of a dome of 

 unusual strength, and so supported as to re- 

 lieve from pressure the floor of a vaulted 

 chamber beneath. The base of the dome- 

 shaped tooth is slightly contracted, and is 

 implanted in a shallow circular cavity ; the 

 rounded margin of which is adapted to a cir- 

 cular groove in the contracted part of the 

 base ; the margin of the tooth which imme- 

 diately transmits the pressure of the bone, is 

 strengthened by an inwardly projecting con- 

 vex ridge. The masonry of this inner but- 

 tress, and of the dome itself, is composed of 

 hollow columns, every one of which is placed 

 so as best to resist or transmit in the due 

 direction the external pressure. The floor 

 of the alveolus is thus relieved from the office 

 of sustaining the tooth : it forms, in fact, the 

 roof of a lower vault, in which the germ of a 

 successional tooth is in course of develop- 

 ment ; had the crushing tooth in use, rested, 

 as in the Wolf-fish, by the whole of its base 

 upon the alveolus, the supporting plate, gra- 

 dually undermined by the growth of the new 

 tooth, must have given way, and been forced 

 upon the subjacent delicate and highly vas- 

 cular and sensitive matrix of the half-formed 

 tooth. But the superincumbent pressure 

 is exclusively sustained by the border of 

 the alveolus, whence it is transferred to the 

 walls dividing the vaulted cavities containing 

 the germs of the new teeth ; the roofs of 

 these cavities yield to the absorbent process 

 consequent on the growth of the new teeth 

 without materially weakening the attachment 

 of the old teeth, and without the new teeth 

 being subjected to any pressure until their 

 growth is sufficiently advanced to enable them 

 to bear it with safety ; by this time the sus- 

 taining borders of the old alveolus are under- 

 mined, and the old worn-down tooth is shed. 

 The singular and powerfully developed 

 dental system of the Wolf-fish (Anarrhi- 

 c/ias Lupus) has been a subject of interest 

 to many anatomists. The general character 

 and physiological relations of the teeth in this 

 species had not escaped the attention of 

 Hunter. In his paper on the Gillaroo trout, 

 read before the Royal Society in 1774, he ob- 

 serves that " the teeth of fishes which subsist 



* fig. 544 ; and art. PISCES, Vol. III., fig. 513, p. 978. 



