66 ON THE DEVELOPMENT OF THE ENAMEL 



which have broken away in the preparation from the more thoroughly 

 calcified segments constituting the enamel deposit on the denticles. 

 It is, in fact, the layer which has been supposed to be at once the 

 functionless ' membrana praeformativa ' of Raschkow, and the func- 

 tionally protective, however otherwise physiologically inert, ' cuticula 

 dentis? or ' Nasmyth's membrane. 5 



If now, in the third place, we take a thin microscopic section of 

 the anterior part of the lower jaw of a fetal calf, made in a sagittal 

 direction, so as to show several developing teeth of various ages in 

 siltt, we are enabled easily to recognise the representatives of the 

 various structures visible to the naked eye in the molar tooth of the 

 elephant, and to harmonise the apparently conflicting statements, 

 which have been made, as to the relations held by the tissue forming 

 the enamel prisms, on the one hand, to the stellate tissue of the 

 n on- vascular enamel organ, and, on the other, to the vascular tooth- 

 capsule. In such a section of a tooth, in which the enamel has 

 already begun to be deposited, we can see the factor of the enamel 

 organ, which is made up of stellate, loosely-compacted anastomosing 

 cells, the so-called ' spongy substance/ occupying or forming a trian- 

 gular area with the apex upwards. The apex of this triangular space 

 marks the lowest level to which the formation of enamel has advanced 

 in its progress downwards from the summit of the tooth. Above this 

 point, or, in other words, where the formation of the enamel has 

 called for an abundant supply of mineral matter, the non-vascular 

 stellate tissue has disappeared, and allowed the vessels of the tooth- 

 capsule to come into close relation with the enamel-forming cells 

 which draw so largely upon what they contain. Below this 

 point the stellate tissue gradually re-assumes its original propor- 

 tions, and in a section of the lateral portions of the spoon-shaped 

 incisors of the calf it may be seen to pass completely round the 

 calcifying dental pulp from its buccal to its lingual surface. The 

 area occupied by this stellate tissue corresponds, of course, to the parts 

 of the cavities of the capsular processes, which lie below the level 

 of the enamel deposit on the denticles ; the disappearance of the 

 stellate tissue in the molar of the elephant, and the separation in 

 that preparation of the upper part of the capsule from the depositing 

 enamel, are alike what the Germans call artefacta. 



Much of what has been advanced in this short paper may be 

 found explicitly or implicitly stated in some one or other of the 





