THE BEAVER 



68 1 



Fig. 97.— Cheek-Teeth of 

 Beaver (iJ times life size). 

 Reproduced from Miller's Cata- 

 logue, by permission of the 

 Trustees of the British Museum 

 (Nat. Hist.). 



The young incisor widens rapidly towards the pulp cavity; at a few 

 millimetres from the unworn tip, the posterior enamel dies out, that of 

 the anterior surface alone persisting; when wear reaches this point 

 the chisel-like cutting edge, so characteristic of the adult incisor, is 

 speedily produced. The milk-molars are in 

 the general form of their crowns and roots 

 strongly reminiscent of the teeth of more 

 primitive Sciurids — and indeed of those of 

 other ancient rodents, e.g. Titanomys among 

 the Lagomorpha. They and the permanent 

 cheek-teeth have, when quite unworn, tuber- 

 cular caps; as the coronal tubercles wear 

 away the prismatic structure of the deeper 

 tooth-levels is revealed. In adult stages of 

 wear the crowns of the cheek-teeth are 

 squarish, the upper teeth being slightly 

 broader than long, the lower rather longer 

 than broad. Each upper tooth has typically 

 three narrow re-entrant enamel folds starting 

 from the outer border, and a single wider fold 

 from the inner side. In lower teeth the 

 pattern is similar, but the arrangement is 

 reversed, the three narrow folds being internal, the single wider one 

 external. All the folds persist until a very advanced stage of wear has 

 been reached. The enamel is smooth and uncrimped, although, in aged 

 specimens, a moderate plication sometimes appears in one or other of 

 the folds. Short roots are developed late in life. 



Dimensions in millimetres of skull: — Adult, Mildenhall, Suffolk, 

 Alluvium (B.M. 85.8.4.1) — Condylo-basal length, 142; zygomatic 

 breadth, 106-4 > interorbital constriction, 30-4 ; mastoid breadth, 69 ; 

 occipital depth, 42-8; length and greatest width of nasals, 61-4x29; 

 diastema, 48; maxillary tooth-row, 33-6; mandible, 109; mandibular 

 tooth-row, 36-8. 



Status : — C. fiber is now extinct in Britain. Attempts have been 

 made to introduce the Canadian Beaver, and these have succeeded in 

 showing that there is no serious difficulty as regards the possibility of 

 acclimatisation. The Marquess of Bute introduced Canadian Beavers 

 to Bute in 1874 and 1875 ; the colony, although now extinct, was in 

 a thriving condition for a good many years, and the keeper, Mr J. S. 

 Black, published an interesting account of it {_Journ. Forestry, February 

 1880); this account has been fully quoted by Harting {Extinct Brit. 

 An., 52). Some were turned down at Sotherley Park, Wangford, 

 Suffolk, but their dams were destroyed as an eyesore, and the last 

 seems to have been killed about 1872 (Harting, op. cit., 59). More 

 VOL. II. 2 X 



