ae 
THE BEAVER 681 
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. 7ztanomys 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 jong, the lower rather longer 
than broad. Each upper tooth has typically Baavins Gk “mea, We Geel 
three narrow re-entrant enamel folds starting Reproduced from Miller's Cate- 
from the outer border, and a single wider fold /ogue, by permission of the 
from the inner side. In lower teeth the Trustees of the British Museum 
pattern is similar, but the arrangement is (\*: Mist: 
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, 61-4 x 29; 
diastema, 48; maxillary tooth-row, 33-6; mandible, 109; mandibular 
tooth-row, 36:8. 
Status :—C. fiver 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, of. czz., 59). More 
VOL. II. 2x 

Fic. 97.—CHEEK-TEETH OF 
