2004 
VOSS ET AL.: BOLIVIAN MARMOSOPS 1% 

EERE CEE 
se | 
Fig. 6. Ventral view of left ear region in Marmosa murina (A, AMNH 267368) and Marmosops 
pinheiroi (B, AMNH 267346) illustrating generic differences in the presence/absence of a secondary 
foramen ovale. In Marmosa, the mandibular branch of the trigeminal nerve (V°, reconstructed course 
shown by heavy arrow) emerges from the endocranial lumen via the foramen ovale (fo), which is 
bordered by the alisphenoid (als) and the petrosal (pet); the extracranial course of the nerve is unen- 
closed in this taxon. In Marmosops, however, the extracranial course of V° is partially enclosed by a 
bony strut (st) that extends from the anteromedial surface of the tympanic wing of the alisphenoid (twa) 
across the transverse canal foramen (tcf); the nerve then emerges from a so-called secondary foramen 
ovale. Other abbreviations: bs, basisphenoid; bo, basioccipital; ce, carotid canal; ect, ectotympanic. 
ricular pelage is only microscopically visi- 
ble). Laid back alongside the head, the short 
mystacial vibrissae do not extend to the tips 
of the pinnae. A small patch of almost-naked 
skin on the midline of the throat suggests the 
presence of a weakly developed gular gland 
in all of the male specimens examined. The 
metacarpals and metatarsals are covered with 
dark (brownish) hairs, but the digits of both 
manus and pes are abruptly whitish. All of 
the males we examined have a knob-like gla- 
brous tubercle on the lateral aspect of the 
wrist that is absent in both females. The scro- 
tal epithelium is pigmented (mottled-grayish 
in preservative) and sparsely covered by 
brownish fur. Both female specimens have 
4—1—4 = 9 abdominal-inguinal mammae. 
Body fur extends onto a short (ca. 1 cm) seg- 
ment of the tail base, but the remainder 
(>90%) of the tail is virtually naked and 
covered by epidermal scales in predominant- 
ly spiral series. Under high magnification 
(25-50), each caudal scale is seen to have 
three hairs projecting from its posterior mar- 
gin; the central hair is visibly thicker than the 
lateral hairs, but perhaps not quite twice as 
wide. On the dorsal surface of the tail, these 
hairs are no more than one to two scale rows 
long, but they are longer (three to four scale 
rows) on the ventral caudal surface. The ex- 
posed caudal epithelium is dark (grayish) 
above and below basally, but it is indistinctly 
bicolored (dark above, pale below) for at 
least half the length of that organ, and the 
tail-tip is entirely white for the last 1-3 cm. 
In dorsal view the skull is distinctively 
proportioned with small orbits, narrow zy- 
gomatic arches, and a very broad interorbital 
region. The nasal bones are long and con- 
spicuously widened posteriorly near the max- 
