560 MR. M. F. wooDWAUD ON [May 5, 



The discovery by Leche (9) of the extremely variable nature of 

 the upper deciduous canine (Plate XXIV. fig. 9, dc.) forms the key- 

 to his conclusious, for this enabled him to perceive that the milk 

 set were in part undergoing reduction, and to formulate the belief 

 that the kiiob-like labial growth of the dental lamina which he found 

 in connection with i^^ was the last trace of the enamel-organ of the 

 milk ]H'edeces8or of that tooth : from this he concluded that the 



milk predecessors to the following teeth ; 2 c pni 1 ^^^ ^^^" 

 entirely suppressed. 



The conclusions may seem very bold, but their correctness is 

 proved beyond a doubt by the two stages which I have been for- 

 tunate enough to obtain. 



Taking as a starting-point the upper canine, I find that 

 in my younger stage the eniimel-orgaii of the permanent canine 

 (p^.) is in a very baclivvard condition, whereas labially a small 

 tooth is developing (fig. 1, do.; see also Leche, Taf. iv. figs. 41 

 -50) ; from the condition of this latter structure it is possible that 

 it might develop into a small fimctional milk-tooth (fig. 9, ^), 

 and from its position and general relationship it is obviously the 

 milk-canine. In the older stage we note (fig. 1 a, p£-) that the 

 enamel-organ of the permanent canine is more developed, and that 

 attached to the labial side of the neck of this structure, i. e. the 

 dental lamina, is a slight outgrowth, indenting which is a small 

 irregular calcification (dc-) ; this is in the position of the germ of 

 the deciduous canine of the younger stage, and evidently repre- 

 sents that tooth in a more advanced condition, i. e. as regards 

 calcification, but at the same time retrograded, for it is so small and 

 irregular that it could not become a functional tooth and probably 

 would not even cut the gum. Thus we see that the canine may 

 vary from a functional tooth (Leche) to a minute irregular calci- 

 fication of no physiological importance {cf. figs. 9 & 1 a, dc.). 



Considerable doubt has been expressed at one time or another 

 concerning the exact homology of the first upper maxillary tooth 

 of Erinaieus, its form in the permanent series being so unlike that 

 of a ty])ical canine, for the reason that it possesses indications 

 of two fangs ; moreover, it is apparently situated a considerable 

 distance behind the premaxillo-maxillary suture. If, however, a 

 young skull be examined (fig. 9), we find that the deciduous canine, 

 whea present as a conspicuous tooth, bears but a single fang and is 

 situated close to the suture, as also is the developing permanent 

 canine, the apparent change in position of the latter tooth being 

 due to the forward extension of the maxilla, growing so as to 

 embrace the premaxilla both labially and on its palatal border 

 (fig. 9 a) ; thus the external premaxillo-maxillary suture in the adult 

 is apparently situated far in front of the canine tooth. The 

 true position of this tooth can be ascertained even in an adult skull 

 if the palatal aspect of the latter be examined, then the canine 

 is seen to be situated almost within the true suture and certainly 

 not far behind it. 



