510 Mr. Owen on the Labyrinthodons 



bifurcation and process. The main radiating fissures extend to within a line or 

 half a line of the periphery of the tooth, and suddenly dilate at their terminations 

 into canals, the areas of which in transverse section are subcircular, oval, or pyri- 

 form ; the branches of the radiating fissures, which are continued into the lateral 

 secondary plates or processes of the dentinal lamellae, likewise dilate into similar 

 and generally smaller spaces. All these spaces or canals in the living tooth, must 

 have been occupied by corresponding processes of the vascular pulp ; they consti- 

 tute as many centres of radiation of the fine calcigerous tubes, which, with their 

 uniting clear substance, constitute the dentine. 



If the dilated spaces of the comphcated and ramified pulp-cavity of the Lahy- 

 rinthodon's tooth were isolated, and their respective systems of calcigerous tubes 

 circumscribed by a coat of caementum, then the tooth of the Labyrinthodon would 

 present the type of that of the Orycteropus, and of the Myliobates, Pristis, and many 

 other cartilaginous fishes : or on the other hand, if the pulp-cavities of the compo- 

 nent cylindrical denticles of the tooth of the Orycteropus were connected together 

 by lines converging to and uniting in a common centre, then it would somewhat 

 resemble the peculiar type of dental structure presented by the Labyrinthodon. 



It would be foreign to my present purpose to pursue the description of the tooth 

 of the Labyrinthodon into the modifications of the dentinal tissue, as displayed by 

 the higher powers of the microscope ; sufiice it to say, that the dentine everywhere 

 presents the structure of fine calcigerous tubes, obeying in their course the usual 

 law, i.e. radiating or converging, with primary curvatures and secondary undulations 

 at right angles, or nearly so, to the surface of the dentine which the cement invests. 



The number of these calcigerous tubes, which are themselves the centres of minor 

 ramifications, defies all calculation ; their diameter is y^ooth of a Une, with inter- 

 spaces equal to seven diameters of their cavities*. 



It has already been stated, that among the few teeth presumed to be reptilian 

 from the Warwick sandstone, the small, conical, externally striated one, figured in 

 the memoir of Messrs, Murchison and Strickland (Geol, Trans, vol, v. PI, XXVIII, 

 fig. 8.), bears the nearest resemblance to the teeth of the German Labyrinthodon or 

 Mastodonsaurus ; it is however much smaller, and the cone is broader and shorter, 



I have subsequently received a larger tooth from my friend Dr, Lloyd, which 

 was discovered in the Warwick sandstone at the Coton-end Quarry, This tooth 

 still more closely resembles in size and form the teeth of the Labyrinthodon figured 

 by Professor Jaeger, especially the smaller specimens (figs, 5. and 6. PI. IV. of 

 his above-cited work) ; it differs only in being somewhat more compressed at the 



* Their general disposition is shown in a section of one of the simple lateral processes of the radiating 

 plates of dentine, in Plate LXI V, A, fig. 2, of my ' Odontography.' The undulation and ramification of the 

 terminations of two of the calcigerous tubes, magnified 650 diameters, are figured at Plate LXIV.A.fig.3, 



