636 
APPENDIX B. (OWEN ON TEETH OF ICHTHYOLITES.) 
however, between this labyrinthic structure and that of the teeth of the Dendrodus is easily discerned, and 
I had the satisfaction to perceive in the microscopic sections of the Russian teeth all the characteristics 
of the teeth of the Dendrodus. 
The longitudinal section in the opposite Plate, fig. 2, shows the entire body of the tooth, permeated by 
the vascular canals, ramifying with apparent irregularity, and anastomosing by their peripheral branches 
in fine loops. The characteristic disposition of the vascular canals or sinuses is shown in the magnified 
view of the quadrant of the circular transverse slice, at fig. 3. 
The pulp-cavity, a, a, has been converted by a coarse kind of ossification into an irregular group of 
large medullary canals of a less cylindrical figure than in the Dendrodus biporcatus : these canals or pro- 
cesses of the pulp-cavity are connected together by a network less close and complex than in the Dendr. 
biporcatus . From the circumference of the central network finer medullary' canals, or vertical sinuses, 
radiate at pretty regular intervals to the periphery of the tooth. Most of these canals divide once, and 
some twice in their course ; the bifurcation taking place commonly near the periphery of the tooth, the 
branches slightly diverging. From each ray and its primary bifurcations short branches are given off at 
brief intervals, generally at right angles with the trunk, or slightly inclined towards the periphery of the 
tooth ; these primary branches more seldom subdivide than in the Dendr. biporcatus, but terminate, as in 
the teeth of that species, by angular dilatations something like leaves, which resolve themselves into 
radiating fasciculi of calcigerous tubules. Each of these systems of radiating tubules constitutes a lobe 
of the dentine, which is separated from the adjoining lobes by an extremely delicate line, representing 
the cemental constituent of the tooth. The lobes of dentine continued from the terminal dilatations of 
the medullary rays are the largest and most regular in form. The extremely minute dentinal tubes ter- 
minate in a linear series of calcigerous cells ; such lines being continued or reflected inwards from the 
periphery of the tooth, and doubtless form the remains of processes of the capsule of the tooth-matrix, 
which inclosed and, as it were, defined the lobes of dentine. 'Hie inflected line of minute cells may be 
traced to near the central reticulate system of large medullary canals. The external longitudinal fine 
grooves on the surface of the tooth indicate the entering lines or fissures filled by the fine cellular cement. 
The close analogy, and at the same time the difference — at least specific — between the tooth of the 
Russian Dendrodus Murchisoni (mihi) and of that from the Scotch Old Red Sandstone will be at once 
seen by comparing figs. 3 and 5 in the opposite Plate. 
Thus, the formerly supposed organic evidence of the supra-carboniferous nature of the sandstones of 
Livonia and Reval is completely negatived by the proof, that the problematical teeth are not those of 
reptiles or air-breathing Vertebrata ; and, at the same time, positive proof has been obtained that they 
belong to the same peculiar genus of extinct sauroid fishes which has been hitherto only recognised as a 
fossil of the Old Red Sandstone. 
The practical importance, independently of geological theory, of determining the relations of the red 
sandstone systems, in reference to the beds of coal which in many countries may be sought for with 
success under the Newer Red Sandstone and Zechstein (Permian), but can never be found beneath the 
Old Red or Devonian, places the value of the microscopic test of the nature of fossil teeth in a striking 
point of view ; for if other proofs had not been obtained of the age of these deposits so extensively 
spread over Livonia and Northern Russia, this tooth alone would have decided the question. 
R. Owen. 
February 20, 1844. 
