On some Anomalies in the Dentition of Phoca hispida

Variation with regard to the dentition is perhaps a more common occurrence among the Seals than among most other groups of Mammals. It is quite probable, that this stands in connection with the more or less reduced condition of the teeth of these animals. The variation in the dental formula can make itself known in several different ways. In his valuable book “Materials for the Study of Variation” BATESON has recorded a great number of dental anomalies among Pinnipedia, concerning in one case the incisors, and in the others the premolar-molar series. Although the author quoted worked with material from different parts of the world and belonging to various genera and species, he does not appear to have known any Phoca hispida with abnorm dentition. Already 1878 the Danish Zoologist SAHLERTZ had, however, the opportunity of reporting about such and found that among 76 skulls of this species not less than 5 presented greater or smaller anomalies. One of these was purely pathological, in the other cases there were found one or two supernumerary premolars or molars. Some time ago I had the pleasure of receiving from my friend Dr. O. NORDQVIST, Director of the Fisheries Bureau, several lower jaws of as well Phoca hispida as Ph. vitulina, which had been delivered for receiving bounties. It is especially the former of these, which are of interest with regard to their dentition because they display very great anomalies. In most cases it is the premolars and molars, which are subjected to variation, as will be described below, but there is also a specimen, which presents a most interesting anomaly with regard to the incisors. It has namely not less than six well developed incisors. The animal has been rather young when killed, with a length of the lower jaw amounting to only 85 mm. (115—122 mm. in old animals). In consequence of the youth the incisors are crowded, but they are all of nearly equal size and none of them gives the impression of being on the way to become suppressed. The arrangement is, as the photographic reproduction (fig. 1) proves, regular on both sides, and the crowding has resulted in the pressing backwards of i2 out of the row, somewhat behind the others. It is of interest to state, that such an arrangement, i. e. the pressing backwards of i2 is fully in accordance with the situation of the incisors in the Otters and also in musteline and viverrine Carnivora etc. generally in such cases, when the incisors are crowded