380 ON THE DENTITION OF THE ARMADILLOS. [JuilC 11, 



4. In a skull (No. 911b, Brit. Mus.) rather smaller though more 

 mature than the last, the seven milk-teeth described in the last spe- 

 cimen are in place and much worn at their summits ; there is also a 

 small cylindrical posterior or eighth tooth in each side of each jaw. 

 Of the milk-teeth, the first is the smallest, being much compressed, 

 the second is rather broader, the remainder considerably broader and 

 nearly equal. The upper ones are pointed, being bevelled in front 

 and behind. The lower ones are worn mostly on the outside, and 

 have a much more acute apex than the upper ones. The fangs of all 

 are closed at the base, and more or less hollowed by absorption on 

 the inner side, this absorption proceeding sometimes so far as to 

 give a two-rooted appearance to the tooth. At the bottom of each 

 alveolus (as is easily seen when the milk-tooth is removed), and at its 

 inner side (in both jaws), is a distinct recess, in which lies the cal- 

 cified conical apex of the germ of the permanent tooth, the outer 

 surface of which lies against the hollowed part of the root of the 

 milk-tooth. These germs are all of nearly equal development. 

 The length of the longest upper milk-tooth, from apex to base, is 

 0""22, of the longest lower one 0""25. The length of the tooth-line 

 in each jaw is 0""7. The milk-teeth are slightly smaller than those of 

 the adult, but otherwise differ very little from them in appearance. 

 They have, however, the important difference of the closure of the 

 base of the fang, causing arrest of growth. The eighth tooth ap- 

 pears to have no predecessor, and consequently is the only true 

 molar. 



Professor Gervais's observation supplies the next stage ; judging 

 from the size of his figure, the animal must attain almost to the dimen- 

 sions of the adult before the milk-teeth are finally shed. The ap- 

 pearance of double roots which he describes is due only to the 

 absorption of the middle part of the fang, in consequence of the 

 pressure of the growing permanent tooth, which, as in other Mam- 

 malia, is placed, in the early stages of growth, not immediately below, 

 but to the inner side of the milk-tooth. 



A striking exception has thus been shown to a widely accepted 

 generalization. The question naturally arises. Is this really the only 

 exception, and is the generalization itself a sound one ? It is most 

 desirable that the teeth of other species of Armadillo should be 

 examined ; but it is a singular circumstance that so insufficient are 

 our public zoological collections, that I have not yet been able to 

 find a single example of the right age to throw any light on this 

 question. All available specimens are either too old or too young. 

 With the exception of the one species above described, all state- 

 ments in reference to the succession of the teeth of these animals 

 appear to rest upon no sufficient basis of observation. 



