On the structure of teeth, and the resemblance of ivory to bone, as illustrated by microscopical examination of the teeth of man, and of various existing and extinct animals / by Professor Owen.
- Owen, Richard, Sir, 1804-1892.
- Date:
- [1838?]
Licence: Public Domain Mark
Credit: On the structure of teeth, and the resemblance of ivory to bone, as illustrated by microscopical examination of the teeth of man, and of various existing and extinct animals / by Professor Owen. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
6/16 (page 140)
![KIGIITI! UEl’OUT 18S8. ivory commence. Tlie superficies of tlie tooth is slightly punctated, but the depressions do not correspond with the mouths oV tubes, but with the interspaces of whole groups of the coarser tubes. Psammodus.—A transverse section of the tooth of this genus pre- sents the appearance, under a moderate magnifying power, as if it were composed of close set coarse tubes, the arese of which were thus ex- posed. Such a section, viewed with a power of 400 diameters, shows that these tubes are surrounded by concentric lamellae, exactly as the Haversian canals; and that these lamellae, and the clear interspace, which is generally equal to the thickness of the lamellae, are permeated by minute irregularly disposed tubes, Avhich anastomose in the clear interspace, and open into extremely minute cells, scattered in the same ]>art. A longitudinal section of the same tooth shows the whole course of the canals ; they run nearly perpendicularly to the convex super- ficies of the tooth, and, consequently, incline outwards at the sides of the section. They lie nearly parallel with each other, with interspaces equal to from 6 to 8 times their own diameter, and branch dichoto- mously once or twice in their course. Each canal is surrounded by concentric layers of a dark colour, encroaching upon one-third of the interspace, which thus presents two dark streaks and one intermediate right line: the whole of these interspaces is perforated by the irregular wavy, branched, anastomosing calcigerous tubes. The terminations of the canals near the periphery of the tooth are slightly dilated, and give off' in every direction calcigerous tubes corresponding to those in the interspace of the canals. The structure of the tooth of Psammodus differs from that of Acrodus in the greater number and more parallel course of the canals, their fewer branches, and want of anastomoses, and in the absence of a distinct external enamel-like layer of very fine tubes. Ptychodus lalisstnius.—The structure of this tooth has a close affinity to that of Psam?nodus : it is composed of Haversian canals and cal- cigerous tubes proceeding therefrom. The base of the tooth is com- ])0sed of close-set and irregular canals, and is very opaque : the canals emerge from this part half-way to the grinding surface, to which they jjroceed perpendicularly. They differ from those of the Psammodus in being wider, more close-set, and more branched,—the branches being given off at more open angles, and the terminal ones being larger in proportion to the trunks. The papillose surface of the tooth is com- posed of the terminations of the inextricably interwoven fine calci- gerous tubes given off from the terminations of the canals. The inter- spaces of the canals are also occupied by the same minute anastomosing reticulate tube-work. Numerous minute calcigerous cells are also present in the interspaces. There is a clear substance coating the grinding surface of the tooth, in which neither tubes nor any definite structure could be detected, though, from analogy, such doubtless exist. The darker substance, forming the concentric lamellee around the canals, occupies the same proportion of their interspace as in the Psammodus. Chimara.—The tooth of this fish apjiears, wiicn a section of it is](https://iiif.wellcomecollection.org/image/b2239087x_0008.jp2/full/800%2C/0/default.jpg)
