II-THE ANATOMY OF THE FUR, SEAL. 



THE DENTITION OF THE FUR SEAL. 

 By Pebdeeic a. Lucas. 



The dentition of the adult fur seal Is i., f, c, i, pm., |, in., f, the conical premolars 

 and molars all having simple roots, a well-developed cingulum on the inner side; and 

 a small accessory cusp on the anterior face. 



In a fetus .taken April 22 the milk dentition is complete, consisting of i., f, c, |, 

 m., |. The incisors are vety minute, particularly the inner upper incisor, and there is 

 no trace of a third lower incisor, although proper microscopic examination of a younger 

 fetus might reveal it. So far as has come under my observation (five specimens at 

 full term), the milk incisors are shed before birth, and this is doubtless often or usually 

 the case with the milk molars and lower milk canines. In a full-grown fetus the lower 

 canines were simply hanging to the gum, as were also the minute second and third 

 lower milk molars; but in other fetal specimens and in some recently born animals 

 the lower milk canines and lower and upper third (last) milk molars were still in place, 

 as shown in PI. I, fig. 1. These last are situated directly over the fourth premolars, 

 so that in Gallorhinus the third milk molars have vertical successors. The first and 

 second milk molars of the fetus are sometimes mere spicules loosely attached to the 

 gum. In other instances they are well formed though small teeth lyiug external to the 

 second and third premolars. The order of appearance of the permanent upper teeth 

 is as follows: incisors 1, 2, 3, premolar 1, premolar 2 and molar 1 (although sometimes 

 the molar is slightly in advance of the premolar), premolar 3, premolar 4, molar 2. 



In the lower jaw the incisors appear first and tlie premolars and molars in regular 

 order from before backwards, the first and second premolars appearing almost 

 simultaneously and slightly before the corresponding upper premolars. The canines 

 appear at about the same time as the second true molar, but not until premolars 1 

 and 2 are well through. There is, however, considerable irregularity in the develop- 

 ment of the teeth, for in some individuals the last milk molar and lower mil^ canines 

 are retained for a fortnight or more after birth. 



The teeth mature more rapidly in the female than in the male, for while the entire 

 tooth row, including the canines, are fully developed in the 2-year-old female, the 

 canines do not attain their maximum size in the males until the age of 4 or 5 years, 

 at which time, or possibly a little later, the true molars have already begun to show 

 some slight signs of absorption. There is also a decided increase in the length of the 

 tooth row of the males between the ages of 1 and 6 of from five-sixteenths to five- 

 eighths of an inch, with the natural result that in old animals the teeth are farther 

 apart than in the young. (Compare figs. 1, 2, 3.) The changes in the jaw itself are 

 much more marked than in the teeth, for this continues to increase in size and weight 

 after the fifth year, this change being one of the important factors in the fighting 

 abilities of the adult males. 



