Recherches sur les Poissons Fossiles. 



325 



An epiderm is constantly found beneath a plastering of this 

 mucous, which last is easily produced by spirits of wine ; the 

 coagulated mucous being raised, the epiderm is found, al- 

 though some authors have erroneously denied its existence in 

 fishes ; it is indeed very thin and transparent, and bears a re- 

 semblance to the epithelium, which lines the mucous coat of 

 the alimentary canal. Nevertheless, in fishes covered with 

 imbricated scales, it forms of itself the folds which envelope 

 the posterior extremity of each scale, so that it covers as 

 much of the internal surfaces, as of the external ; but it is 

 chiefly in fishes whose scales are very small and emersed 

 in the skin that its existence is easily demonstrated, on 

 raising the coagulated coat of mucous formed by alcohol, 

 and with which it is covered. 



From the foregoing considerations, we are also to regard 

 the teeth as dermatic formations, of which the bulb is a spe- 

 cies of malpighien gland, and which might be treated of 

 in this place ; but I prefer referring their examinations to the 

 head of Osteology, on account of some observations on their 

 growth in different modifications of the dentary system, which 

 I would wish first to conclude, so as to be able to refer to 

 certain peculiarities of the skeleton with which it is necessary 

 to be previously acquainted, in order that the singular 

 disposition presented by the teeth may be treated more 

 completely in connection with the point of their insertion. 



The scales of the greater part of fishes are imbricated one 

 upon another as tiles : that is to say, those of the anterior 

 series rest their posterior border on the anterior border of 

 the series following; and this imbrication still leaves unco- 

 vered a part of the scales more or less considerable, not 

 alone of their posterior border, but also of their superior 

 and inferior borders. This overlying gives to the scales 

 their apparent form, which is very often quite different from 

 their true contour ; for an oblong scale is covered so far in 

 front and rear, that its height may seem to exceed the length, 



