ANATOMY OF VERTEBRATES. 



263 



buried in the membrane from which they rise, and the surface 

 to which their basis is attached becomes the bottom of a 



closed sac : but this sac 

 does not become inclosed in 

 the substance of the jaw ; 

 so that teeth at diiferent 

 stages of growth are 

 brought away with the 

 thick and S(jft gum, when 

 it is stripped from the 

 jaw-bone. The final fixa- 

 tion of teeth, so formed, 

 is effected by the develope- 

 ment of ligamentous fibres 

 in the submucovis tissue be- 

 tween the jaw and the base 

 of the tooth, which fibres 

 become the medium of con- 

 nection between those parts, 

 either as elastic ligaments 

 or by continuous ossifica- 

 tion. Here, therefore, is 

 represented the ' follicular ' 

 stage of the developement 

 of a Mannnalian tooth : 

 but the ' eruptive ' stage 

 takes place without pre- 

 vious inclosure of the follicle and matrix in the substance of the 

 jaw-bone. 



In BaUstes, Scarus, Sphyraiia, the Sparoids, and many other 

 Fishes, the formation of tlie tcctli presents all the usual stages 

 which have been observed to succeed each other in the dentition 

 of the higher Vertebrates : the papilla sinks into a follicle, becomes 

 surrounded by a capsule, and is then included within a closed 

 alveolus of tlie growing jaw, figs. 259, 261, c, where the develope- 

 ment of the tooth takes place and is followed by the usual eruptive 

 stages. A distinct enamel-pulp is developed from the inner 

 surface of the capsule in BaUstes, Scarus, Sarffus, and Chri/so- 

 jihi'i/s. 



In the formidable Barrncada {Sj)Ii>/>-ana) the loss or fracture of 

 the lancet-shaped teeth, in the conflict witli a struggling ]irey, is 

 re|iaired by an uninterrupted succession of new puljis and toctli. 

 The existence of these is indicated by tlie foramina, which are 



Verticnl section of jaw and tuL'tb [Laii, 



