OCR Text |
Show 252 PROF. FLOWER ON HYDROCHCERUS CAPYBARA. [May 6, The species of Reptiles recognized as hitherto known to occur the Solomon Islands were stated to be 19, and those of Batrachians 9 in number. This paper will be published in the Society's ' Transactions.' The following papers were read:- 1. Note on the Dentition of a young Capybara (Hydrochmrus capybara). By Professor W . H. F L O W E R , LL.D.; F.R.S., P.Z.S., &c. [Eeceived April 7, 1884.] As is well known, the incisors of the simplicident Rodents no milk predecessors. With regard to the molars, the rule seems to be the following. When there are only three (as in the Common Rat), or fewer than three (as in Hydromys), these are all true molars, and have no predecessors. These animals then are truly monophyodont. When the number exceeds three, it is by the addition of teeth to the front of the series, which are premolars and are preceded by milk-teeth. In the large majority there is only one such tooth on each side. When milk-teeth are present, a remarkable variation is observed in their characters and the period at which they are matured and shed. Thus in the Guinea-pig and its allies the one milk-molar (a small, though tolerably well-formed tooth) is absorbed or shed a short time before birth ; while in the Porcupines and Beavers the corresponding tooth is retained until the animal has nearly reached the adult condition \ On Nov. 30, 1875, two Capybaras were born in the Society's Gardens: one died on the same day, the other lived until the 8th of December. The skull of this one was preserved, and is now in the Museum of the Royal College of Surgeons. It shows the state of dentition at this early age particularly well. In the adult Capybara the dental formula is i. j, c. g, p. j, m. ^ = the distinction between premolars and molars being inferred from tbe analogy of other Rodents, in fact of other placental Mammals. In the little animal eight days old, the cranium of which measures 102 millim. in length, the number of the teeth is just the same as in the adult ; the incisors and four molariform teeth being all present and in an equal state of development. A small portion of the surface of each, including the posterior molar, has been already abraded by wear. The molar teeth show the same form and pattern as in the adult, being each divided by deep lateral grooves into distinct lobes corresponding to those of the full-grown tooth. They are, however, all very much smaller, the length of the whole series 1 See " Notes on the First or Milk Dentition of the Mammalia," by W . H. Flower, Transactions of the Odontological Society of Great Britain, iii. 1871 pp. 211-232. |