Professor Owen on the Teeth of the Labyrinthodon. 317 



ordinary laws of dental structure are, however, strictly adhered to, 

 and every space intercepted by a convolution of the folds of the 

 cement is occupied by corresponding processes of the dentine. 

 These characters were presented by a transverse section of a frag- 

 ment of a tooth of the Labyrinthodon Jaegeri from the German 

 Keuper, which included about the middle third part of a tooth, 

 and Mr. Owen considers that the entire length of the tooth might 

 be 3^ inches, and the breadth at the basis l£ inch. 



The external longitudinal grooves, which correspond to the in- 

 flected folds of the cement, extend upwards from the base of the 

 tooth to about three-fourths of its height, decreasing in number as 

 the tooth diminishes in thickness, and disappearing about half an 

 inch from the summit of the tooth. Each fold of cement penetrates 

 less deeply as the groove approaches its termination ; and Mr. Owen 

 conceives that the structure of the upper part of the tooth may be 

 more simple than that of the lower, but he has not yet been able 

 to extend his investigations to it. 



The dentine consists of a slender, central, conical column or 

 " modiolus," hollow for a certain distance from its base, and radi- 

 ating outwards from its circumference a series of vertical plates, 

 which divide into two, once or twice, before they terminate at the 

 periphery of the tooth. Each of these diverging and dichotomizing 

 vertical plates gives off throughout its course narrower vertical 

 plates, which stand at nearly right angles to the main plate, in rela- 

 tion to which they are generally opposite, but sometimes alternate. 

 Many of the secondary plates, which are given off near the centre 

 of the tooth, also divide into two before they terminate. They par- 

 take of all the undulations which characterize the inflected folds of 

 the cement. 



The central pulp-cavity is reduced to a line, about the upper third 

 of the tooth ; but fissures radiate from it, corresponding in number 

 with the radiating plates of the dentine. One of these fissures is 

 continued along the middle of each plate, dividing where it divides, 

 and penetrating each bifurcation and process ; the main fissures ex- 

 tend to within a line or half a line of the periphery of the tooth ; 

 the terminations of these, as well as the fissures of the lateral pro- 

 cesses, suddenly dilating into subcircular, oval, or pyriform spaces. 

 All these spaces constitute centres of radiation of the fine calcige- 

 rous tubes, which, with their uniting clear substance, constitute 

 the dentine. The number of these calcigerous tubes, which are the 

 centres of minor ramifications, defies all calculations. Their diameter 

 is the ^noo^ 1 °f a bne, with interspaces equal to seven diameters of 

 their cavities. 



Mr. Owen then compares the structure of the section of a tooth 

 procured in the sandstone of Coton-End Quarry, and lent to him by 

 Dr. Lloyd of Leamington. The tooth nearly resembles in size and 

 form the smaller teeth of Labyrinthodon figured by Prof. Jager. All 

 the peculiarities of the labyrinthic structure of the Keuper tooth are 

 so clearly preserved in this specimen, that the differences are merely 

 of a specific nature. 



