MILK-DENTITION. 483 



tooth,* intermediate in size between the permanent and decid- 

 uous molars. The true milk-teeth are I. |^ij, C. [[, M. |=|; 

 the upper are all much smaller than their representatives of the 

 lower series, the canine and incisors forming merely minute 

 cylindrical calcined points. The molars are also very small, 

 consisting of little rootless dentinal caps, the middle one the 

 larger, with indications of two roots. The lower molars are not 

 only several times larger, but have conical, pointed crowns, 

 and two long, distinct roots, especially the first and second. 



Steenstrup gives the milk-dentition of both Phoca grcenland- 

 ica and P. fcetida as I. \^_\, C. ~-J, M. jj-"^. The lower molars 

 and the second and third upper are distinctly two-rooted ; the 

 upper, however, are many times smaller than the lower, the 

 first upper consisting of merely -a minute rootless crown. 



Four fo3tal specimens of Phoca fcetida, collected by Mr. Lud- 

 wig Kurnlien on the late Howgate Polar Expedition, show the 

 upper, as well as the lower, molars to be all two-rooted, but 

 through the process of absorption the anterior fang of the up- 

 per molars early disappears, in one specimen the upper molars 

 consisting of minute crowns, with an oblique posterior fang. 

 The lower molars are several times larger than the correspond- 

 ing teeth of the upper series, and are all distinctly two-rooted ; 

 the third, or posterior, is much the larger, and is distinctly 

 tricuspid, there being a well-developed secondary cusp on each 

 side of the larger principal one. In the specimen in which the 

 fangs of the upper molars have become partly absorbed, the ca- 

 nines and incisors are wholly wanting. In the others the canines 

 are present ; one has all the lower incisors, but only one of the 

 upper incisors. Most of the incisors, both above and below, 

 had, in the other examples, either been wholly absorbed, or were 

 lost in the preparation of the specimens. The upper canines are 

 directed horizontally forward, forming a large angle with the 

 permanent .canines beneath them, and consist of small cylinders 

 two-tenths of an inch long and about two-one-hundredths in 

 thickness. The lower canines are somewhat larger, and are 

 directed obliquely upward and forward. 



In Halichcerus, according to Nordmann, a foetal specimen gave 



the following formula: 1. 1}^ - rEi M - 5|- rj ^ he milk-molars 



* This is the view maintained by Reinhardt (Vid. Medd. f. d. Naturh. 

 Forening f. 1864 (p. 259), aud to which Steenstrup (Ibid., pp. 269-274) 

 seems to substantially accede. 



