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THE OTTAWA NATURALIST > 



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Vol. XXI. 



OTTAWA, iMAY, 1907 



No. 2 



NOTE ON THE OCCURRENCE OF A SUPERNUMERARY 



TOOTH IN A DOG.* 



By Lawrence M. Lambe, F.G.S., F.R.S.C., Geological Survey 



of Canada. 



Last summer whilst engaged in field work in the vicinity 

 of Kamloops Lake, B.C., the writer found, near the mouth of 

 Tranquille River, the skull of a dog, probably that of a collie, 

 that is of some interest. In this skull the teeth of the mandible 

 appear to be normal, but in the upper jaw a supernumerary first 

 premolar is present on both sides. 



J Natural size 



Between the second premolar and the canine (see the above 

 figure) are two small, single-rooted teeth with simple conical 

 crowns. Of these the one next behind the canine, and separated 

 from it. by a space measuring 3.3 mm., is apparently the normal 

 first premolar. Between this tooth and the second premolar is 

 the tooth considered to be the supernumerary one. It is sHghtly 

 smaller than the first premolar, and its posterior edge is less 

 sloping ; in other words, its crown, in side view, is more bilaterally 

 symmetrical, a point possibly not sufficiently accentuated in the 

 figure. It almost entirely occupies the interval between the first 

 and second premolar, touching the latter but leaving a very 

 narrow space between it and the former. The other teeth in the 

 upper jaw, including the incisors, are apparently quite normal. 



In comparison with the skull of a white wolf (Cams lupus 

 occidentalis var. albiis) from Fullerton, Hudson Bay, the 

 Tranquille specimen is slightly shorter with almost the same 



* Communicated by permission of the Acting Director of the Geologi- 

 cal Survey of Canada. 



