A Caliper Modification for Measuring Skulls and Bones

538
JOURNAL OF MAMMALOGY
Vol. 43, No.4
GENERAL NOTES
A CALIPER MODIFICATION FOR MEASURING SKULLS AND BONES
Measuring a large series of skulls or other bones by ordinary use of a vernier caliper can
be tedious and time consuming. The special mounting device for holding a vernier caliper
shown in Plate I enabled the writer to make 1,900 measurem ents of mink skulls and femurs
in approximately 2 days.
The essence of the design is to anchor th e caliper in a fixed position, provide flat parallel
surfaces perpendicular to the axis of m easurement , provide a positive operating linkage and
a simple set of optics to facilitate reading the vernier from a sitting position.
Perhaps the most critical aspects of construction are to be found in the accuracy of
cutting the several surfaces. However, final assembly steps compensate for small errors in
achievin g p erpendicularity between locating surfaces. As much of the cutting as possibl e
should be done with circular saw adjusted for accuracy with test cuts on a scrap block .
Final finishing on a large, flat sanding surface and with an 8-inch fine file proved satisfactory.
The construction of the model shown allows for 50.0 mm of stock between each caliper
blade and the measuring surface. This technique of construction simplifies positive location
of measuring surfac es relative to caliper blades at the sacrifice of reading the scale directly.
Therefore, a correction factor of minus 100 mm is applied to all readings.
An alternate mounting technique would be to make an accurate cut in the measuring
face to receive the caliper blade to such depth as to permit a flush relationship with the
caliper blade. Set screws from the top of the blocks could then be applied to anchor
measuring surfac es coincident with a zero setting of th e caliper.
Final adjustment is accomplished in assembly by the following sequence of steps: (1)
anchor fixed block in place, (2) locate and anchor securely sliding block to moveable caliper
blade, (3) locate fixed blade on fixed block and close calipers tightly allowing tail of caliper
to float in space, (4) shim tail block to meet caliper without disturbing its position, (5)
anchor tail block in place, (6) apply tail locating pin with care not to move caliper horizontally and (7) tighten fixed blade and tail anchoring screws .
PLATE I
A caliper device for measuring skulls and bones.
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Nov. 1962
GENERAL NOTES
LENS
SCREW-STRAIGHT
CLAMP SLIDING BLOCK
.
539
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rt?
I
LEVER
FIXED
SlOCK
11
.
1
··
1
FIG. I.-An exploded drawing showing construction details of the caliper modification
for measuring skulls and bones.
These steps insure parallelism between measuring faces. Operating handle and linkage
should offer no problems. Construction details are shown in Fig. 1. A list of materials
used included the following with dimensions' taken from the finished model: 1 pc
plywood-5 ply-~" X 7*" X 131h ", 1 pc hard maple-I" X 2" X 3", 1 pc hard maple
-I" X 2" X 2", 2 pc hard maple-I" X I" XI", 1 pc hard maple-lh" X lh" X 11M",
1 pc hard maple-I" X 1" X 4", 1 pc fir-%" X I" X 7 1.4", 1 pc sheet aluminum-20 gal
<*2") 1%" X 4", 1 pc mirror-;i6" X %" X 1:tA,", 1 pc coat hanger wire-16 gal (%4")
6" long, 1 Helios 5" or 12 cm vernier caliper, 1 pc 5 penny finishing nail (locating pin),
2 round head wood screws-l h ", 1 round head wood screw (straight thread) I:tA,", 7 flat
head wood screws 1%" and 1 pocket lens (I%: diam. focal length 2 in.).-CHARLES KINSEY,
Minnesota Division of Game and Fish, St. Paul. Received 21 January 1961.
[Contribution from the Minnesota Division of Game and Fish, Pittman-Robertson Project
W-II-R, St. Paull, Minnesota.]
HYBRIDIZATION BETWEEN THE BLACK-TAIL DEER AND THE
WHITE-TAIL DEER
Throughout a large part of western North America the black-tail and white-tail deer are
sympatric. In some areas there is a difference in habitat selection, but in many parts of
the common range the two species can be seen together through the breeding season. It is
a matter of interest therefore, that there are apparently no recorded instances of hybridism
in the wild state.
In captivity it has been shown that the two species will mate successfully. Ackermann
( 1898) reported by Gray (1954), refers to hybridization between unstated subspecies of
male white-tail deer and female black-tail in the Cincinnati Zoo. An anonymous author
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