The baculum is the bony part of the penis. In the species of the
subgenus _Neotamias_ the proximal part of the baculum is termed the
shaft, and the distal upturned part is termed the tip. On the dorsal
side of the tip there is a longitudinal ridge termed the keel. The
proximal end of the shaft is termed the base (see fig. 19). Depending on
the species, the shaft varies from 2.11 to 5.28 mm. in length, and the
base may or may not be widened or deepened.
The purpose of this report is to: (1) Show the usefulness of the
structure of the baculum as a taxonomic character in chipmunks; and (2)
compare a classification based on the structure of the baculum with a
classification based on the structure and appearance of the skull and
skin.