212 LABYRINTHODONTS. 



size towards the anterior portion of the jaw ; the posterior teeth, 

 which are shghtly compressed at their base in the antero-posterior 

 direction, present at that part about a line and a half in diameter ; 

 the anterior ones measure half a line across the same part ; the length of 

 some of these small anterior teeth above the sockets is three lines, they 

 are terminated by a sub-acute apex. The sockets do not lie between 

 parallel lines ; the alternate ones are placed a little more internally. 

 The teeth were present chiefly in the more external sockets ; but 

 where they remained in both, the row of teeth presented the same 

 slightly zig-zag disposition. The sockets of the teeth are more 

 shallow in the present than in the preceding fossil ; the outer alveolar 

 wall is rather more developed than the inner, and the anchylosed bases 

 of the teeth more nearly resemble in their oblique position those of the 

 existing Batrachians. The teeth are directed slightly inwards, and are 

 probably received, like those of the Menopome, into the interval 

 between the maxillary and vomerine series of the upper jaw, when the 

 mouth is closed. 



The fine external striation and fluting is confined to the basal 

 third of the tooth, as are also the labyrinthic inflections of the 

 external cement. Above this part, the dentine consists of fine 

 calcigerous tubes, radiating from the linear remains of the pulp- 

 cavity at right angles to the surface of the tooth ; being parallel 

 with the axis of the tooth, where they form its apex, and gra- 

 dually inclining outwards until they become transverse to that 

 axis, which is their general disposition in the body of the tooth, 

 between the apex and the commencement of the inflected verti- 

 cal folds of the cement. At its apical part, therefore, the tooth 

 of the Labyrinthodon resembles in the simplicity of its intimate 

 structure that of the entire tooth of the ordinary Batrachia and 

 of most reptiles. The vertical inflected processes of the cement are 

 at first short and straight, occurring at pretty regular distances 

 around the circumference of the tooth ; so that here the tooth par- 

 takes of the structure which has already been said to characterize 

 the base of the tooth of the Ichthyosaurus. Soon, however, the 

 primitive inflected folds of cement sink deeper into the dentine and 

 commence their undulating course, and as the tooth expands, 



