EXISTENCE OF AN ENAMEL ORGAN IN AN ARMADILLO. 45 



With the subsequent stages in the development of the 

 teeth Ave are not for the present concerned ; the prominent 

 feature of Arnold and Goodsir's view, which was long adopted 

 by ahnost every writer, was the appearance, in the first place, 

 of a free, uncovered papilla, which was afterwards destined to 

 be calcified into dentine. 



As expressing the matter clearly and concisely, I may 

 quote the words of Professor Owen : ^ 



" In the development of a tooth a matrix or formative 

 organ, corresponding iu complexity with the kind of tooth 

 to be formed, is first developed. It consists either of a soft 

 vascular papilla — a free conical process — as in certaiu fishes, 

 which mould of the future simple tooth is called its ' pulp,' 

 or • the dentinal pulp,' or it consists of the inilp enclosed 

 in a ' capsule,' or of a inilp xoitli such a modification of its 

 peripheral part^ situated between the pulp proper and the 

 capsule, as to merit a distinct definition as an '' enamel 

 organ.' ^\xq. first and most constant of these parts is termed 

 \\vQ ^ dentinal pidp ^ \\i^ second is the capsule or ' cemental 

 pulp,' and the third is the ' enamel pulp.' " 



To this I may add that the simplest teeth consist only of 

 dentine, the next stage in complexity being the addition of 

 cementum, Avhile the presence of enamel marks a third 

 stage in complexity; so that it would be quite in accordance 

 with the little that we know of the laws of development that 

 in an animal whose teeth ultimately possess all three struc- 

 tures the dentine germ should appear first, next that of the 

 cementum, and lastly that of the enamel ; it would, in fact, 

 then be an illustration of '^ progress from the general to 

 the special in development." 



But unfortunately more accurate observations do not con- 

 firm this. The order of appearance of the three several germs 

 is not by any means that above described, and the researches 

 of Professors Kolliker and Emil Dursy have shown (1) that 

 there is never at any time a deep, widely open groove, from 

 the bottom of which spring up free, uncovered papillae, but 

 that the " primitive dental groove," as seen and described by 

 Arnold and Goodsir, was ^'artefact ;" and (2) that at a period 

 •when the dentine germ has no histological characters, but is 

 only distinguishable from the surrounding tissue as a slight 

 opacity of no very definite form nor definite limits, the enamel 

 germ has undergone active growth and very manifest histo- 

 logical differentiation of its component cells (see fig. 2). 



Thus, although a skilled observer can detect faint indica- 



' Article "Odontology," ' Encyclopsedia Britaunica,' p. 41i. The 

 talics are my own. 



