The Medals of Creation, Volumes 1 and 2 / First Lessons in Geology and the Study of Organic Remains

by Gideon Algernon Mantell

Lign. 222. Upper Tooth of the Iguanodon: nat. size.
Wealden. Brook Bay, Isle of Wight.
The crown is worn down to an oblique smooth surface, and the fang is absorbed.

Jaw and Teeth of the Iguanodon. Ligns. [219-223].—Although the form and structure of the cranium are unknown, yet the half of a lower jaw, discovered in Sussex by Capt. L. Brickenden,[640] and a fragment of an upper jaw, found some years since,[641] enable us to form a tolerably perfect idea of the structure and functions of the dental organs of the Iguanodon. The unused tooth of this reptile is characterized by the prismatic form of the crown, the presence of from two to four longitudinal ridges on its enamelled face, the denticulated margins ([Lign. 221], a), and finely serrated edge of the summit, as seen in [Lign. 220], fig. 3. The shank or fang of the tooth (Ligns. [221], [223, fig. 2]) is sub-cylindrical, slightly curved, and tapers to a point. The inner surface of the crown in the lower teeth, and the outer surface in the upper, are covered with a thick layer of enamel, but the opposite face of the crown and the sides have but a thin coating of this substance. The teeth of the upper jaw ([Lign. 222]) are curved in the opposite direction to those of the lower, and have the convexity external, and the concavity internal. Thus the upper and lower molars were related to each other nearly as in the Ruminants; the outer aspect below corresponding to the inner above (see Petrif. Lign. 56, p. 254). The specimens met with have almost always the apex of the crown more or less worn down by use[642] (see [Lign. 223]), and presenting an oblique, triangular, smooth surface, as in the fine large specimen figured in [Lign. 221], which was found imbedded in the trunk of a Clathraria, as if it had snapped off while the animal was in the act of gnawing the tough stem. The denticulated margins are well developed; in fig. 1, they appear as simple serrations; but viewed laterally, they are seen to be formed by a series of denticulated plates ([Lign. 223], fig. 6). The crown of a tooth of a young animal, worn at the summit, and presenting but three longitudinal ridges, is represented [Pl. VI. fig. 4a]. The microscropical structure consists of a simple pulp-cavity in the centre of a body of dentine permeated by calcigerous tubes, but with this peculiar modification, that the dentine is traversed by vascular canals, radiating at definite intervals from the pulp-cavity nearly to the periphery of the tooth, and running parallel with the calcigerous tubes; thus constituting a softer and coarser dentine than in the other reptiles, and resembling that which characterizes the teeth of some of the herbivorous mammals.[643] The crown of the tooth is covered with a layer of enamel, which is thickest on the external surface: and the fang is invested with cement. The structure here described is shown in [Pl. VI.]; fig. 4b, a vertical, and fig. 4c, a transverse section of a tooth, seen by transmitted light, with a high magnifying power. The calcigerous tubes are ¹/₂₅₀₀₀ an inch in diameter. Sections of the teeth of the Iguanodon are beautiful objects under the microscope, for the medullary canals are generally of a deep yellowish brown colour.

[640] Figured and described in the Phil. Trans. 1848, p. 188, pl. xvi. xvii.

[641] Both specimens are fully described in Petrif. pp. 242, et seq.

[642] Plates iv. and xvii. in the "Fossils of Tilgate Forest," contain representations of upwards of thirty specimens of teeth in various states of development and detrition.

[643] Tomes on the Microscopic Structure of the Tooth of the Iguanodon, Petrif. pp. 239, 240. See also Owen’s Odontography, p. 249, and pl. lxxi.; and Cycl. Anat. Art. Teeth.

Lign. 223. Teeth of Iguanodon. Wealden. Tilgate Forest.