BULLETIN FLORIDA STATE MUSEUM


ranges from 10.0-11.3 for Mesohippus to 7.2-8.9 for Equus. This same
index for Florida N. phlegon ranges between 9.3-10.2, which is greater
than Hussain's study predicted for advanced three-toed horses. The
proximal surface, which articulates with the navicular, is concave and
has a well-developed medial non-articular groove, which is poorly
developed or absent in such primitive horses as Mesohippus or
Parahippus. The distal articular surface has two (dorsal and lateral)
confluent ectocuneiform facets, one cuboid facet, a non-articular area,
and one mesentocuneiform facet. In the Florida N. phlegon specimens
the mesentocuneiform facet and lateral-most portion of the ec-
tocuneiform facet are confluent, as in Hipparion illustrated by Hus-
sain (1975:199, Fig. 7C).
 The right and left medial (III) metatarsals are represented by UF
22630 and UF 22620, respectively (see Fig. 9, Table 9). The proximal
articular surface is transversely wider than it is anteroposteriorly long
and bears two large ectocuneiform facets (dorsal and plantar), one


TABLE 8.-MEASUREMENTS OF NAVICULARS OF Nannippus phlegon FROM FLORIDA.
Specimen AP length Width Index*
UF 21324, Right 26.0 28.1 9.3
UF 10697, Left 28.2 29.2 9.7
UF 21322, Left 27.6 27.2 10.2
*Ratio length/width x 10 (Hussain 1975).



 A B
 c e









 0 1 2 3 4 5cm


FIGURE 12.-Right navicular, UF 21324, of Florida Nannippus phlegon from Santa Fe
River 1A. (A) proximal articular surface (dorsal view); a, astragalar facet; b, non-
articular area; (B) distal articular surface (plantar view); c, cuboid facet; d, ec-
tocuneiform facets; e, mesentocuneiform facet; f, non-articular area.


Vol. 25, No. 1