DENTAL CHARACTERS OF AUSTRALIAN RATS. 587 



29. On the Dental Characters o£ certain Australian Rats. 

 By Prof. F. Wood Jones, Adelaide University. 



[Received May 22, 1922 : Read June 13, 1922.] 



(Text-figures 1-12.) 



The observations recorded in the present paper, although very 

 limited in their scope, may possibly prove to be of some value 

 when they are extended over a wider range of types than is avail- 

 able to the author. 



The business of diagnosing the specific characters of the 

 material which he studies does not, as a rule, fall within the 

 province of the anatomist, but there are times when even 

 the teacher of human anatomy has to enlarge his field of enquiry, 

 and enlarge it so that he comes within measui-able distance of 

 being a systematic zoologist. The attempt to assign a specific 

 name to an Australian Murine is an enterprise no amateur 

 should engage in, and it must not be thought that the present 

 author is responsible for the determination of the species men- 

 tioned here. But short of giving an actual name to a species, it 

 may happen that one who is not a systematic zoologist may want 

 to track down, as nearly as possible to its proper position, some 

 animal into the structure of which he is enquiring. 



Among the characters which bulk lai-ge in the diflferential 

 diagnosis of various Murines are the crown patterns of the molar 

 teeth. It is quite certain that not a tithe of the literature 

 dealing with the molar patterns of the rats has been reviewed 

 during a search of the works and periodicals available here in 

 Adelaide ; but enough has been studied to convince the author 

 that although it is a simple thing to diagnose the crown occlusal 

 pattern of the molars of a young animal, it is difiicult or even 

 impossible to say what may have been the pattern when once the 

 molars are worn down in an old or an aged specimen. Text-fig. 8 

 illustrates the condition of the left upper molar series in three 

 individuals belonging to one species, and it is "easy to see that in 

 the oldest individual a diagnosis of the original occlusal pattern is 

 a matter of considerable uncertainty. Consideration of the inter- 

 esting problem of the relation of crown-pattern to root-formation 

 has prompted the author to turn to the root-patterns in order to 

 see if they presented any constant or useful featiu^es. 



A series of circumstances has led up to this little investigation 

 of the root-patterns of a few Australian rats. In the first place, a 

 number of skulls and certain cranial fragments were found uporr 

 an island, — Franklin Island in ISTuyt's Archipelago, — the living- 

 rats inhabiting which had been already properly identified. The 

 skulls were all of aged individuals, and no diagnosis could be made 

 from the molar patterns; and yet it was of some importance 

 that the identity of the fragments should be sufficiently well 



