Baculum

Definition and stakes

John A. White,  The Baculum in the Chipmunks of Western North America

“ Eutamias sonomae Grinnell
Figure 4
Upper parts rich reddish, more or less dulled by gray; backs of pinnae of ears nearly bare; tail long and bushy; size large; skull large, long, and narrow; rostrum deep.
Baculum: Shaft thin; keel low, 1/10 of length of tip; tip 27 to 31 per cent of length of shaft; angle formed by tip and shaft 130°; distal 1/4 of shaft slightly compressed laterally; base deeper and wider than shaft; shaft of medium length, 3.03 to 3.30 mm.; ridges on either side of tip strongly developed, partly obscuring keel from side.
”
Source: Gutenberg

John A. White,  The Baculum in the Chipmunks of Western North America

“ Variation with age.—In the chipmunks the baculum varies but little with age. In the youngest specimens that I have taken, the M3 and m3 have not yet erupted and there is no wear on P4 and p4; nevertheless, the baculum in these specimens has nearly an adult configuration and size. In juvenal Eutamias minimus the tip of the baculum is longer in relation to the length of the shaft than it is in adults; the tip is 18 to 28 per cent of the length of the shaft in adults, as opposed to 29 to 32 per cent in juveniles. ”
Source: Gutenberg

Robert L. Packard,  Speciation and Evolution of the Pygmy Mice…

“ The length of the baculum of B. musculus (average of 58 specimens without regard to subspecies) is contained in the length of the body (of specimens from which the bacula were removed) 22.7 times, a figure approaching that in Ochrotomys. When bacula of both species of Baiomys were compared to those of O. nuttalli, bacula of B. musculus were found to most closely resemble those of O. nuttalli. The baculum of a single [Pg 605] specimen of Calomys (C. laucha) was contained in the length of the body 15.5 times. ”
Source: Gutenberg

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