1882]. the Enamel of the Teeth in Vertebrates. 



159 



Here, as is frequently the case, the ends of the cells appear broken or 

 vacuolated, or striated, and with high power the striae can be distinctly- 

 seen in transverse section on the edge of the membrane, which in all 

 stages, being much more tenacious than the enamel cells, generally 

 adheres to the enamel when the cells are removed, and may be raised 

 up by the use of acid. As a rule, the older the tooth the more com- 

 pletely the reticulations or the cell-markings are obliterated, and the 

 more resisting is the membrane, so that by maceration, as well as by 

 the help of an acid, it may be taken off entire from the surface of the 

 young tooth. It has been isolated by myself in this way, as also by 

 Hertwig, who asserts it to be the " derb " basement membrane, and 

 the " zellzeichnungen" upon it to be simply the impressions of adjoin- 

 ing cells. Preparations similar to fig. 3 clearly disprove this, and the 

 basement membrane, when it can be demonstrated, is far from a 

 "derb" structure, as will be shown further on. 



Kolliker* says — " The ends of the enamel cells taken from the 

 enamel present different appearances. Some are simply cut off 

 squarely, others possess smaller (myself, Hertz) or larger ("Waldeyer) 

 clear layers of the same breadth as the cells (the enamel fibres in 

 process of formation), still others, finally, have pointed ends, with or 

 without such layers (Tomes, Waldeyer, Hertz). I consider these 

 ends, which I also have seen, as artificial products — that is, as 

 accidentally detached parts of the yet unfinished enamel fibres." If 

 Kolliker had seen them on the firm dense membrane, as in fig. 3, or 

 fig. 2, he could not have held this opinion. An extended and careful 

 study leaves no room for doubt that this membrane, forming in many 

 cases the cuticula of placoids and the cuticula dentis of both mam- 

 malia and fishes, is made by the metamorphosed ends of the enamel 

 cells. But the cuticula has not always precisely this structure either 

 upon the tooth or on the placoid ; apparently more or less of the so- 

 called enamel cells may enter into its formation. This, at least, is 

 certain, the cuticla, or " Schmelz oberhautchen," may not only have 

 upon its surface the " cell markings," but it may be formed of entire 

 cells (or at least of enough to include the nuclei) which have under- 

 gone a greater or less differentiation into horny tissue, obscuring 

 more or less completely the outlines of the nuclei. Such a cuticula 

 is shown in situ on the placoid represented in fig. 4. It is entire upon 

 the under surface of the scute, which is more protected ; upon the 

 upper side fragments only are left. A high immersion lens showed 

 distinctly on parts of the membrane, the outlines of cells and their 

 nuclei (fig. 5) and the membrane could be traced into the columnar 

 layer of epithelial cells at the base of the spine. 



The cuticula of the mammalian tooth has several times been found 



* Kolliker, " Handbuck der Grewebelehre," p. 385. 



