234 ON THE DEVELOPMENT OF THE TEETH 



In all these animals I have examined the smallest teeth I could 

 find perfectly entire, without any rough mechanical' treatment, which 

 I should think would destroy the delicate membrane. 



In the Frog, its surface is in parts reticulated, as in Man , in the 

 Mackerel and Skate {figs. 9, 12) I have been unable to find any such 

 reticulation. In both these the enamel forms a conical cap of almost 

 structureless or obscurely fibrous substance at the extremity of the 

 tooth, while the layer upon the body of the tooth is very thin.^ In 

 the Skate it is thick, dense, yellowish, structureless, and perfectly 

 smooth ; but in the Mackerel it is developed upon the lateral edges of 

 the young tooth into sharp notched processes ; lines stretch across the 

 body of the tooth from these, not unlike the contour lines one sees on 

 the enamel of a young human tooth. 



A membrane, corresponding with that which has been described in 

 the human subject then, is also found in members of each of the other 

 groups of Vertebrata which possess teeth. In the human subject, and 

 in Mammals, this membrane was discovered, and very accurately 

 figured and described, fourteen years ago (that is, in January, 1839, in 

 the ' Medico-Chirurgical Transactions), by Mr. Nasmyth, under the 

 name of the " persistent capsular investment." No question has ever 

 been raised as to the right of Mr. Nasmyth to this discovery ; but it is 

 remarkable, that neither in Professor Owen's ' Odontography,' which is 

 the first subsequent work upon the teeth, nor in Professor Kolliker's 

 ' Mikroskopische Anatomie,' which is the last, is there any notice of 

 Mr. Nasm}'th's discovery. Kolliker, indeed (/. c, pp. "jQ, Tj), describes 

 the structure as " schmelz-oberhautchen," but his description is not so 

 good as that of Nasmyth, and he states that it does not extend over 

 the cement — Nasmyth having shown that it does. Unfortunately, 

 however, the latter, like all who have succeeded him, misled by the 

 supposed mode of development of the enamel from the enamel-organ, 

 imagined that as the " persistent capsule " was outside the enamel it 

 could be nothing else than the membrane of the dental capsule ; and 

 hence the erroneous description of the adherence of the latter to the 

 crown of the tooth, which I have already quoted. Had he chanced to 

 examine a tooth before its eruption, he would at once have seen the 

 incorrectness of his hypothesis. 



^ As this "dense exterior layer" may be dissolved out by dilute acid, leaving the 

 " membrana propria of the pulp," which is very much thinner, standing, it is quite clear 

 that it is not " formed by the calcification of the membrana propria of the pulp, which 

 therefore precedes the formation of ordinary dentine." — {Odontograpliy, p. 17). Why 

 should it not be called enamel ? It has at least as much claim to this title as that of the 

 Frog. 



