On the development and homologies of the molar teeth of the wart-hogs (Phacochoerus) : with illustrations of a system of notation for the teeth in the class Mammalia / by Professor Owen.

  • Owen, Richard, Sir, 1804-1892.
Date:
1850
Catalogue details

Licence: Public Domain Mark

Credit: On the development and homologies of the molar teeth of the wart-hogs (Phacochoerus) : with illustrations of a system of notation for the teeth in the class Mammalia / 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.

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    The grinder, which is the subject of figs. 2 and 3, tab. xix., is the last molar from the right side, lower jaw, of the Phac. of the natural size. To determine whether any successional teeth were developed above or beneath the fangs of pre-existing teeth destined to be displaced by such development, in other words, wliether a true deciduous series and a premolar series of teeth existed in the Wart-Hogs, required an examination of the jaws of an individual younger than the youngest specimen examined and figured by Home. The subject of Plate XXXIII. fig. 1 of the present communication is of the required immaturity, and, with the other specimens to be described, supplies those links in the series which were wanting for the explanation of the entire course of the truly remarkable dentition of the genus Phacochoerus. Fig. 1 shows a side view of the teeth in the young Phac. jPHiani; the grinding surface of the molar teeth in use is given, from the upper jaw in fig. 2, and from the under jaw in fig. 3. These teeth include all the milk-molars which are developed, together with the first permanent true molar. The milk-molars are 3 —3 in number in the upper jaw, and 2 — 2 in the lower jaw. The first true molar, m 1, is also fully developed and in use in both jaws. The summit of the second true molar {m 2) is just appearing above the socket. The length of the skull exhibiting this instructive phase of dentition is 10 inches. The milk-molars answer to the teeth of the typical dentition symbolized hy d2, d3, and c? 4 in the upper jaw, and to c? 3 and c?4 in the lower jaw. The first is implanted by two fangs, the second by three, the third by four fangs; the shape of these teeth is sufficiently illustrated by the figures. Their rate of increase in size from the first to the last is considerable, yet not equal to that manifested in the true molars. Upon examining the substance of the jaws above the deciduous molars of the upper jaw and beneath those of the lower jaw, two formative alveoli and the trace of a third were detected in the upper jaw, one above d 4, containing the crown of a premolar; the other above d 3, and the rudimental cell above d 2. The matrix, which the latter might have contained, had not begun to be calcified. A small formative socket was found beneath the last milk-molar of the lower jaw containing the crown of a premolar. The gubernacular canal from this socket opened between the fangs on the inner side of the milk-tooth. A second still smaller socket of an anterior premolar was beneath the interspace between the two milk-molars. The true nature of the molar behind the milk-teeth in both jaws was plainly shown by its long fangs extending beyond the parallel of the formative sockets of the suc- cessors of the milk-teeth, and widely open at their ends: this tooth has no vertical successor and is the first true molar, m 1. Only the crown of the second true molar {m 2) is formed at the stage here described ; and a few detached columns of the still larger and more complex third molar (m 3) were all that were calcified in its com- mencing formative alveolus. 3 Q 2