454 MB. M. F. WOODWARD OX MAMMALIAN DENTITION. [May 2 



The enamel-orgau of the 2nd i'linctional incisor (morphological 

 4th) soon loses its connection with tlie gum, and the dental 

 lamina from whicli it is developed does not again obtain any 

 connection with the gum in the incisor region. The enamel-organ 

 of this tooth is too young to show any trace of the successionol 

 tooth, although the examination of other forms (21. fjujanteus and 

 bracJu/urus) show that it is undoubtedly to be referred to the 1st 

 dentition. 



The dental lamina, after giving rise to this tooth, is continued 

 back as a slightly thickened lamina (club-shaped in section) into 

 that backward prolongation of the premaxilla \\hich is situated 

 internally to the maxilla (fig. 29) and in which the 3rd incisor of 

 the adult is developed ; in this region it becomes once more 

 swollen (fig. 4, i'^) to give rise to the latter tooth, which is, however, 

 developed very late in life and therefore hardly shows at this 

 early stage. Halfway between these two teeth and attached to the 

 external (adamantine) face of the dental lamina is situated a very 

 perfectly formed small, pointed tooth ; this is the 3rd rudimentary 

 tooth above referred to (fig. 1, i'). In section this tooth is seen 

 to be well developed, possessing the most highly differentiated 

 enamel-organ, Avhich secretes a thick layer of enamel, iuternal to 

 which is a well-developed mass of dentine surrounding the pulp- 

 cavity. The entire tooth measured '4 mm. long by '25 mm. broad. 

 Its general structure, however, suggests that it is fully formed, 

 and its ultimate fate is probably that of the two anterior vestigial 

 teeth, viz., it is reabsorbed. 



A very important question now arises. Do these two teeth belong 

 to the 1st or the 2nd dentition, and also what is their numerical 

 jjosition amongst the incisors ? In attempting to solve this point 

 it will be ^^•ell to bear in mind Rose's suggestion, viz., that the 

 3rd functional incisor of the adult (<') belongs to the second 

 dentition and is not preceded by a deciduous tooth. 



Fig. 4 represents a Avax model reconstructed from the sections 

 by means of a camera lucida. An examination of this shows that 

 the enamel-organ of this small calcified tooth (i') is situated 

 external to the 2nd and 3rd functional incisors (i* and i'") and 

 connected with the dental lamina by a long neck ; its external 

 position certainly suggests that of a milk-tooth, but on the other 

 hand it is no more nearly related to the 3rd than to the 2nd 

 functional incisor, being situated just about halfway between the 

 two, so that supposing it were a milk-tooth it would be nearly im- 

 possible to say to which tooth it is related. Further, if it belonged 

 to the 1st dentition its enamel-organ should be attached to the 

 dental lamina nearer to the point of origin of the latter from the 

 gum ; whereas in the specimen under consideration these three 

 teeth (i^, i% i'^) all arise from the dental lamina at the same level, 

 which suggests that they belong to the same series and not to two 

 dentitions distinct from one another in point of time, for in that 

 case the one belonging to the 1st dentition would arise from the 

 denial lamina superficially to the corresponding tooth in the 2nd 

 dentition. 



