MILK DENTITION. 221 



found are referable to the Phoeids on tlie one hand, and to the 

 Wah-uses on the other, indicatmg- for the Otariids the same 

 curiously limited habitat as now. 



MILK DENTITION. 



The milk dentition in the Pinnipeds rarely persists much 

 beyond foetal life, and is never to any great degree functional, 

 and the dental formula of the temporary teeth is substan- 

 tially the same in all. In the Walruses, however, two of the 

 posterior ujjper milk molars and the last lower one often remain 

 till a comparatively late period of life, but all traces of the 

 others disappear soon after birth. The two middle pairs of 

 incisors probably never jjierce the gums, and the others scarcely 

 persist beyond the fcetal period. The formula for the temjiorary 

 dentition of this group is usually recognized as I. g^g? C. ^^, 

 M. |5| (or M. ~^). In the Seals, however, the number of 

 molars appears to never exceed ^l . In the Earless Seals " the 

 milk-teeth are extremely rudimentary in size and form, and per- 

 fectly functionless. The majority of them never cut the gums 

 and are absorbed actually before bii-th, and certainly within a 

 week after birth scarcely a trace of any of them remains."* 

 The milk molars are three in number on each side, both above 

 and below, and are replaced respectively by the second, third, 

 and fourth molars of the permanent set. The canines are 

 all represented in the temporary set. The number of tem- 

 porary incisors varies in the different genera, it corresponding 

 apparently with the number in the permanent set. In Phoca 

 vitulina, P. grcenlandica, and P. foetida, they have been found 

 to be 2~2, but the two inner ones of the upper jaw are absorbed 

 long before birth. In the Elephant Seal, Professor Flower 

 found, in a specimen eleven inches long, " a complete set of 

 very minute teeth, viz. I. ^, C. i, M. f , on each side ; all of the 

 simi)lest character."t 



In the Eared Seals, the milk molars are of the same num- 

 ber as in the PJiocinw, namely l^g, and hold, approximately at 

 least, the same position relatively to the molars of the i)erma- 

 nent set. They are separated by wide diastema, and the middle 



* Flowek, " Eeniarks on the Homologies and Notation of the Teeth of the 

 Mammalia," Journ. Phys. and Anat., iii, 1868, p. 269. 

 tibid., p. 271, tig. 4. 



