TEETH. 



881 



struggling prey, is repaired by an uninter- 

 rupted succession of new pulps and teeth. 

 The existence of these is indicated by the 

 foramina, which are situated immediately 

 posterior to, or on the inner margin of, the 

 sockets of the teeth in place ; these foramina 

 lead to alveoli of reserve, in which the crowns 

 of the new teeth in different stages of de- 

 velopment are loosely embedded. It is in 

 this position of the germs of the teeth that 

 the Sphyranoid fishes, both recent and fossil, 

 mainly differ, as to their dental characters, 

 from the rest of the Scomberoid family, and 

 proportionally approach the Sauroid type. 

 The base or fang of the fully-developed tooth 

 of the Splii/rcena is anchylosed to the parietes 

 of the socket in which it is inserted. The 

 pressure of the crown of the new tooth ex- 

 cites absorption of the inner side of the base 

 of the old, which thus finally loses the requi- 

 site strength of attachment ; and its loss is 

 followed by the absorption of the old socket, 

 as in the higher animals. 



It is interesting to observe that the alter- 

 nate teeth are, in general, contemporaneously 

 shed ; so that the maxillary armour is always 

 preserved in an effective state. The relative 

 position of the new teeth to their predecessors, 

 and their influence upon them, resembles, in 

 the Sphyr(Eiw, some of the phenomena which 

 will be described in the dentition of the cro- 

 codilian reptiles. To the crocodiles the pre- 

 sent voracious fish also approximates in the 

 alveolar lodgment of the teeth ; but it mani- 

 fests its iclithyic character in the anchylosis 

 of the fully-developed teeth to their sockets, 

 and still more strikingly in the intimate struc- 

 ture of the teeth. 



In all fishes the teeth are shed and re- 

 newed, not once only, as in Mammals, but 

 frequently, during the whole course of their 

 lives. The maxillary dental plates of Lepi- 

 dosiren, the cylindrical dental masses of the 

 Chima?roid and Edaphodont fishes, and the 

 rostral teeth of Pristis (if these modified 

 dermal spines may be so called) are, perhaps, 

 the sole examples of "permanent teeth" to 

 be met with in the whole class. 



When the teeth are developed in alveolar 

 cavities, they are usually succeeded by others 

 in the vertical direction, as in the pharyngeal 

 bones of the Labroids (fig. 513., art. PISCES, 

 Vol. III. p. 978.) ; but sometimes they follow 

 one after the other, side by side, as in the 

 Scaroids ( PISCES, fig. 516. c, p. 979.). The 

 successional teeth owe the origin of their 

 matrix to the budding out from the capsule of 

 their predecessors of a caecal process, in which 

 the papillary rudiment of the dentinal pulp is 

 developed according to the laws explained 

 in the Introduction to my " Odontography," 

 and the article TOOTH. But, in the great 

 majority of fishes, the germs of the new teeth 

 are developed, like those of the old, from the 

 free surface of the buccal membrane through- 

 out the entire period of succession ; a cir- 

 cumstance peculiar to the present class. The 

 Angler, the Pike, and most of our common 

 fishes, illustrate this mode of dental repro- 



VOL. IV. 



duction ; it is very conspicuous in the carti- 

 laginous fishes, in which the whole phalanx 

 of their numerous teeth is ever marchiii"- 

 slowly forwards in rotatory progress over the 

 alveolar border of the jaw, the teeth being 

 successively cast off as they reach the outer 

 margin, and new teeth rising from the mucous 

 membrane behind the rear rank of the pha- 

 lanx. 



This endless succession and decadence of 

 the teeth, together with the vast numbers in 

 which thej r often coexist in the same fish, 

 illustrate the law of Vegetative or Irrelative 

 Repetition, as it manifests itself on the first 

 introduction of new organs in the animal 

 kingdom, under which light we must view 

 the above-described organised and calcified 

 preparatory instruments of digestion in the 

 lowest class of the vertebrate series. 



At the extreme limit of the class of fishes, 

 and connecting that class with the reptiles, 

 stands the very remarkable genus, the dental 

 system of which is figured in cut 560. This 

 consists of two small, slender, conical, sharp- 

 pointed, and slightly recurved teeth, which 

 project downwards from the nasal bone (c), 

 and of strong trenchant dental plates anchy- 

 losed with the alveolar border of the upper 

 (a) and lower (b) jaws, in each of which the 

 plate is divided at the middle, or symphysial 

 line, so as to form two distinct lateral teeth. 



The office of the two laniariform teeth is to 

 pierce and retain the nutritive substance or 

 prey which is afterwards divided and com- 

 minuted by the strong maxillary dental plates. 



The upper pair of these plates is supported 

 by the anterior part of a strong arch of bone, 

 which combines the characters of the su- 

 perior maxillary, palatine, and pterygoid bones; 

 the superior maxillary is represented by the 

 median and anterior bar, passing in front of 

 the dental plate of the lower jaw when the 

 mouth is shut, terminating on each side in a 

 process which projects outwards and back- 

 wards, as mjig. 560., ., on each side of the an- 

 terior part of the arch ; the palatine portion 

 constitutes the median part of the roof of the 

 mouth behind the foregoing ; the pterygoid 

 portion is indicated by its fulfilling the usual 

 function of an abutment extended between the 

 palatine portion of the upper jaw and the ar- 

 ticular pedicle of the lower jaw ; the upper 

 dental plates are confined to the first two 

 parts of the arch (maxillary and palatine), and 

 do not extend upon the pterygoid portion ; 

 the lower dental plates (b) are anchylosed to 

 the premandibular bone. Viewing the upper 

 pair of plates as a single tooth, it may be 

 described as indented at its outer surface l>y 

 five vertical angular notches, penetrating in- 

 wards through half the breadth of the sup- 

 porting bone, and dividing the plate into six 

 angular processes, which, from the direction 

 and varying form and breadth of the entering 

 notches, radiate from the posterior part of 

 the median line or division of the tooth. The 

 inferior dental plate is similarly notched on 

 its outer side, but the proportions of the an- 

 gular indentations are such, that they receive 



SL 



