940 DR. A. HOPEWELL'SMITH AXD DR. H. AV. MARETT TIMS ON 



views, and we agree with Woodward's first statement that the 

 presence of six upper incisoi's, in spite of all the difficulties which 

 it involves, is " an absolute fact," The one point upon which we 

 join issue with Woodward is his view of the homology of the first 

 functional incisor which he regards as being i. 1, whilst we hold 

 that it is i. 2. The small calcified vestige in both our stages 

 is clearly anterior to and independent of the first large tooth 

 which is obviously the first functional incisor. Our disagree- 

 ment is due to differences of interpretation of the conditions 

 present in a very puzzling region, i, e. close to the median 

 symphysis ; and though we hesitate to put ourselves in opposition 

 to so accurate and experienced an observer, we nevertheless are 

 compelled to adhere to the opinions already stated. We are, how- 

 ever, quite in accord with him in regarding the outer functional 

 incisors as being the 4th and 6th, the 3rd and 5th disappearing. 



We, like Woodward, are therefore at variance with the opinion 

 of Oldfield Thomas (5), who regards the missing incisors ag being 

 the outermost ones of the series. Though Deppendorf (1) does 

 not appear to have examined the jaw of Mac?-opu8, he has made 

 interesting observations on the tooth-genesis in many other mar- 

 supials. In jEpyprymmis he identifies the three functional incisors 

 as the 2nd, 3rd, and 5th. Thus he agrees with us in the identifi- 

 cation of the 1st functional teeth, but differs from both Woodward 

 and ourselves in the identification of the two outermost functional 

 premaxillary teeth. It is unfortunate that there should thus be 

 four different versions given on this subject. Possibly the con- 

 ditions described by Deppendorf may be really different and not 

 merely a difference in interpretation, as he carried out his 

 researches in other genera, in which the relative proportions of 

 the bone may be somewhat different and thus produce different 

 results. 



Lower Incisors. — In the lower jaw we belicA^e there are evidences 

 of five ante-molar teeth. Whether the most posterior one is the 

 vestige of a canine or of an outer incisor, it is impossible to deter- 

 mine. Of the x^emaining four the first three are vestigial, so that 

 according to our interpretation the functional incisor of the adult 

 -is i. 4. This statement is at variance with Woodward's conclusion 

 as to the homology of this tooth which he regards as i. 2. In his 

 illustration he figures two vestiges which obviously correspond 

 with our 6' and c , his first incisor in Petrogale being a minute 

 calcified tooth just as is the germ 5'. The morphological 3rd incisor 

 of Petrogale is " more vestigial than the first," just as c is more 

 vestigial than h' . 



The discrepancies between ovir interpretations probably depend 

 on the following facts. (1 ) Woodward seems to have examined the 

 jaw on one side only, and to do so would have divided it through a,t 

 the symphysis. In doing so he would most certainly destroy the 

 minute vestige a which we have found lying practically within 

 the symphysis. (2) He regards the posterior vestige as being 

 posterior to the large functional incisor, whereas we regard it as 

 being anterior. We both agree in stating that it lies close to the 



