878 



TEETH. 



teeth of the Scarus a fourth substance is 

 added by the ossification of the base of the 

 pulp after its summit and periphery have been 

 converted into hard dentine ; and the teeth 

 (Jig. 558.), thus composed of cement (c), 

 enamel (t), dentine (d), and osteo-dentine, are 

 the most complex in regard to their sub- 

 stance that have yet been discovered in the 

 animal kingdom. 



The tubes which convey the capillary ves- 

 sels through the substance of the osteo- and 

 vaso-dentine of the teeth of fishes* were 

 early recognised, on account of their com- 

 paratively large size ; as by Andre, e.g. in the 

 teeth of Acanthurus, and by Cuvier and Von 

 Born in the teeth of the Wolf-fish and other 

 species. Leeuwenhoek had also detected the 

 much finer tubes of the peripheral dentine 

 of the teeth of the Haddock. These " den- 

 tinal tubuli" are given off from the parietes 

 of the vascular canals, and bend, divide, and 

 subdivide rapidly in the hard basis-tissue of 

 the interspaces of those canals in osteo-den- 

 tine ; the dentinal tubuli alone are found in 

 true dentine, and they have a straighter and 

 more parallel course, usually at right angles 

 to the outer surface of the dentine. Those 

 conical teeth which, when fully formed, con- 

 sist wholly or in great part of osteo-den- 

 tine or vaso-dentine, always first appear with 

 an apex of hard or true dentine. In some 

 fishes the simple central basal pulp-cavity of 

 such teeth, instead of breaking up into irregu- 

 _ar or parallel canals, sends out a series of 

 vertical plates from its periphery, which, when 

 calcified, give a fluted character to the base 

 of the tooth, e. g. in Lepidosteus o.ryurus. f 

 Sometimes such radiating vertical basal plates 

 of dentine are wavy in their course, and send 

 off narrow processes from their sides ; and, 

 as a thin layer of the outer capsule interdigi- 

 tates with the outstanding plates of the den- 

 tinal pulp, and becomes co-calcified with them, 

 a transverse section of such a tooth presents 

 a series of interblended wavy or labyrinthic 

 tracts of thick dentine radiating from the cen- 

 tre, and of thin cement converging towards the 

 centre of the tooth.J An analogous but more 



* The vaso-dentine of Pristls and Mytiobates is 

 like that of the teeth of the Cape Anteater (Orycte- 

 ropus) : the vaso-dentine of the Psammodonts re- 

 sembles that which forms the base of the tooth of 

 the Sloth and Megatherium : the vaso-dentine of 

 Mammals differs from the osteo-dentine in the 

 absence of the radiated "Purkinjian," cells. 



f Wyman, American Journal of Natural Sciences, 

 Oct. 1843. Cuvier has given an accurate view of the 

 plaited structure of the base of the Wolf-fish's teeth in 

 pi. 3-r fit). 7. of his Lecons d' Anatomic Comparee, 

 1805 ; where it is described at the base of the 

 osseous tubercle, which supports the true tooth. 



J This remarkable structure attains its highest 

 complication and forms the largest proportion of the 

 tooth in the gigantic extinct labyrinthoclont Batra- 

 chia, and from which, therefore, I have taken the 

 illustrations of that complex modification of dental 

 structure (Jig. 552 .). I had discovered in 1841 the 

 more simple modification of this structure " at the 

 base of the tooth in a few fishes " (Geol. Trans., 2d 

 series, vol. vi., p. 507), but had not then seen so 

 complex an example in that class as Dr. Wyman 



complicated structure obtains when the ra- 

 diating, wavy, vertical plates of dentine dicho- 

 tomise, and give off from their sides, through- 

 out their course, numerous branch plates and 

 processes, which are traversed by medullary 

 sinuses and canals with their peripheral ter- 

 minations dilated, and becoming the centres 

 of lobes or columns of hard dentine. The 

 transverse section of such teeth gives the ap- 

 pearance of branches of a tree, with leaf-stalks 

 and leaves, radiating from the central pulp- 

 cavity to the circumference of the tooth ; and 

 I have called the fossil fish in which this 

 structure was first detected, Dendrodus. 



Thus, with reference to the main and funda- 

 mental tissue of tooth, we find not fewer than 

 six leading modifications in fishes; hard or 

 true dentine (Sparoids, Labi-olds, Lophius, Ba- 

 tistes, Pycnodonts, Pnonodon, Sphyrtena, Mega* 

 lichthys, Rhizodus, Diodon, Scarus) ; osteo- 

 dentine (Cestradon, Acrodus, Lcpidosiren, 

 C'tenodus, Hybodus, Percoids, Scicenoids, Cot- 

 toids, Gobioids, and many others); vaso-den- 

 tine (Psamnwdus, Chirmsroids, Pristis, Mi/lio- 

 bates) ; plici-dentine (Lophius, Holoptychius, 

 Lepidosteus oxyurus, at the base of the teeth) ; 

 labyrintho-dehtine (Lepidosteus platyrhintts, 

 Bothriulepis) ; and dendro-dentine (l)endro- 

 dus); besides the compound teeth of the 

 Scarus and Diodon. 



One structural modification may prevail in 

 some teeth, another in other teeth of the same 

 fish ; and two or more modifications may be 

 present in the same tooth, arising from changes 

 in the process of calcification and a persis- 

 tency of portions or processes of the primitive 

 vascular pulp or matrix of the dentine. 



The dense covering of the beak-like jaws 

 of the Parrot-fishes (Scari), consists of a 

 stratum of prismatic denticles, standing al- 

 i.iost vertically to the external surface of the 

 jaw-bone. An account of the structure and 

 development of this peculiar armature of the 

 jaws is abridged from my " Odontography " 

 (pp. 11211 6.), in the article PISCES (Vol. 1 1 1. 

 p. 979.). It is peculiarly adapted to the ha- 

 bits and exigencies of a tribe of fishes which 

 browse upon the lithophytes that clothe, as 

 with a richly tinted carpet, the bottom of the 

 sea, just as the Ruminant quadrupeds crop 

 the herbage of the dry land. 



The irritable bodies of the gelatinous 

 polypes which constitute the food of these 

 fishes retract, when touched, into their star- 

 shaped stony shells, and the Scari conse- 

 quently require a dental apparatus strong 

 enough to break off or scoop out these cal- 

 careous recesses. The jaws are, therefore, 

 prominent, short, and stout, as shown in Jig. 

 515. p. 979. Vol. III.; and the exposed portions 

 of the premaxilliaries and premandibulars are 

 encased by the complicated dental covering 

 represented in Jigs. 515 and 516. Vol. III. 



The polypes and their cells are reduced to 

 a pulp by the action of the pharyngeal jaws 



and M. Agassiz (Reeherches sur les Poissons Fos- 

 siles, " Sauroides," 1843) subsequently described 

 and figured, in teeth of the genus Lepidostms. 



