670 Mil. M. r. WOODWARD ON ' [May 5, 



On making an examination of the clarified jaws (Plate XXVI. 

 fig. 29) of aj'oung animal (hairless), one is immediately struck with 

 the correctness of the greater part of these figures, but in respect to 

 the first premolar they appear to be incorrect, for no trace is observ- 

 able of Bate's dpm. 1. In order to be certain that I was not dealing 

 with an abnormal specimen, I examined the clarified jaws of three 

 specimens of about the same age as that studied by Bate, two others 

 being cut one into horizontal and the remaining into frontal 

 sections ; three younger animals were also examined by the section 

 method'. In all 10 half heads were investigated, and as these, 

 obtained from various localities, all agreed amongst themselves in 

 respect to the relations of the 1st premolar, I cannot but come to 

 the conclusion that Bate's observations on this point are erroneous, 



and that the teeth which he describes as ,^' . have no existence. 



In the younger specimen all the deciduous teeth save the 1st 

 premolar were well calcified, but the germs of the permanent teeth 

 though distinct were but little differentiated. An examination 

 of a horizontal section at this period (figs. 27 and 28) shows pm. 1 

 developing in a position precisely similar to that occupied by the 

 reduced deciduous incisor, canines, and premolars ; and, as is the 

 case with the latter, the former exhibits a specialized portion of 

 the dental lamina on its lingual surface, the only observable differ- 

 ence being that dpm. 1 is larger, uncalcified, and generally more 

 backward than the other millc-teeth ; also that the germ of ppm. 1 

 is slighter but might well be thought capable of developing at 

 a later period. That this is not the case is seen from an examina- 

 tion of the older stage : here all the deciduous teeth are strongly 

 developed and even dpm. 1 is now calcified (fig. 31) ; it is, 

 however, verv large and not at all of the nature of a vestigial 

 needle-shaped tooth such as figured by Bate, but rather presents all 

 tlie characteristics of the tooth regarded by him as ppm. 1. The 

 permanent incisor, canines, and premolars (fig. 30) are now highly 

 differentiated, with large enamel and dentine germs : a comparison 

 of one of these with the indication of the germ of ppm. 1 

 (Plate XXVI. fig. 31,rf.Z.), shows that the latter is now less marked 

 than in the earlier stage and is obviously aborting ; consequently we 

 may safely assert that it never attains any degree of specialization, 

 but remains merely a slight swelling of the dental lamina. 



The entire absence of any labial development from that portion 

 of the dental lamina between the large enamel-organ of this tooth 

 (dpm. 1) and the epithelium of the mouth, taken together with the 

 position occupied by it, viz. one similar to Ihat of the true milk- 

 teeth, and the specialized thickening of the dental lamina on its 

 lingual side, exactly resembling in appearance and position the true 



• In all 3 stages were examinee!, including two specimens of stage 1, one of 

 the 2nd, and five of the 3id stage, all being older llian I.eclie's etagea. 



(1) 55 ram. total length ; 17 mm. head length. 



(2) 68 „ ,. „ 18 „ „ 



(3) 95 30 „ „ 



