110 PROFESSOR ROLLESTOM. 



in the preparation from the more thoroughly calcified seg- 

 ments constituting the enamel deposit on the denticles. It 

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

 the functionless " membrana prseformativa " of Raschkow, 

 and the functionally protective, however otherwise physiolo- 

 gically inert, " cuticula dentis,^^ or ''Nasmyth's membrane." 



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

 section of the anterior ])art of the lower jaw" of a foetal calf {see 

 PL VII), made in a sagittal direction, so as to show several 

 developing teeth of various ages in situ, 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 harmonize the apparently conflicting statements Avhich 

 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 non-vascular enamel organ, and, on the other, to the 

 vascular tooth-ca])sule. In such a section of a tooth, in 

 which the enamel has already begun to be deposited, we can 

 see (PL VII, c) the factor of the enamel organ, w^hich is 

 made up of stellate, loosely compacted anastomosing cells, 

 the so-called " spongy substance," occupying or forming a 

 triangular area with the apex upwards. The apex of this 

 triangular space marks the lowest level to which the forma- 

 tion 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 alloAved 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 reassumes 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 linjiual 

 surface. The area occupied by this stellate tissue in PL VII 

 corresponds, of course, to the parts of the cavities of the 

 capsular processes of PL VI, 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 separa- 

 tion in that preparation of the upper part of the capsule 

 from the deposing enamel, are alike what the Germans call 

 a7'tefacta. 



Much of Avhat has been advanced in this short paper may 

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

 the numerous memoirs or treatises on the development of the 

 teeth which have appeared of late. It is believed, however, 



