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

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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$In none of the other members of the Hog family is the first true molar (ml) so much worn down at the corresponding early stage of development of the second true molar, and it is upon this precocious growth of the first true molar that the chief peculiarity of the order of shedding of the teeth of the Phacochceri depends. In the Phac. ^liani, the penultimate and last milk-teeth {d 3, dA) in the upper jaw are displaced and succeeded by corresponding premolars, which therefore answer to ])3 andj9 4 of the typical series. The anterior small milk-grinder, d2, is sometimes succeeded by a minute premolar, but occasionally this is abortive, or absorbed before it cuts the gum. In the lower jaw both milk-molars {d3 and dA) are succeeded by the corresponding premolars p^,pA, at least in the Phac. JEliani. The stage of dentition of the Phac. jPlUani, given in figs. 1, 2 and 3, corresponds with that in the common Hog, illustrated by the teeth in the lower jaw in Plate XX. fig. 1 of the Philosophical Transactions for 1801. In that figure the last grinder in place is the first true molar, m 1; the penultimate is the last milk-molar, dA \ the next is d3, the next c?2; and a little in advance of this, between it and the rudirnental canine, is the small anterior premolar, p 1. The germs of the other premolars, p 2, 3 and pA, are shown in their formative sockets beneath the deciduous teeth they are destined to replace. If the symbols above given be marked upon the teeth in the figure cited, the homo- logies of those in the reduced dentition of the young Wart-Hog will be readily appre- ciated. The teeth developed in the lower jaw of that species are,—c?3, dA, p^, p A and m 1 : in both jaws m 2 has only its crown developed, and m 3 only the commence- ment of its crown. The teeth which are suppressed in the Phac. ^liani are, in the lower jaw, d\, d'2,p\ and p2. In the upper jaw d\ and1 are suppressed, and sometimes also jo2. The next stage of dentition (Plate XXXIV. figs. 4 and 5) shows the shedding of the deciduous molars to be concomitant with the coming into place of the second true molar, m 2 ; it is well illustrated in the cranium of a young PAac. jpllmii from Senegal in the Museum of Comparative Anatomy in the Garden of Plants: in which each of the three deciduous molars of the upper jaw have been succeeded by a premolar {p 2, pS, p 4, fig. 4), and the same with regard to the two deciduous molars in the lower jaw {p 3, p 4, fig. 5). The anterior angle of the crown of the last huge molar has also begun to protrude from the formative alveolus, so that the permanent or 0 0 second molar series now shows j^=22, which is the greatest number of grinders presented at any given time in the genus Phacochoeriis. The first true molar, ni\, is however worn to near the fangs, and its grinding surface, as compared with that in Plate XXXIII. fig. 2, begins to be simplified. The homologies of the teeth at this period are indicated by the symbols attached to them in the figures. The stage of dentition of the young Phac. Pallasii, figured by Home in tab. xix. of his memoir, is a little more advanced than that of the Phac. Pallasii above de-$