BULLETIN FLORIDA STATE MUSEUM


ticular facet for the trapezium. Evidently the trapezium was absent.
Primitive horses normally have a trapezium (Sondaar 1968), and
Chubb (1912) found this bone in 57% of the Equus specimens that he
examined. Matthew (1926) stated that the absence of the trapezium is
one of the characters of Nannippus, which the N. phlegon specimens
from Florida support. The shaft of metacarpal II is three-sided,
relatively slender, and tapers below the proximal articular region.
Again, the distal articular areas are not preserved in these specimens
(see discussion of metapodials below).
 UF 7256 is a virtually complete left femur (Fig. 11, Table 7).
Fragmentary femora are represented by UF 7436 (right), UF 7432
(left), and UF 7435 (left). Proximally the head does not have a complete
and distinct rim, in contrast to the condition seen in Equus (Hussain
1975 for example). The fovea capitus, which serves for attachment of
ligaments, is triangular in outline. As in all horses, the greater, lesser,
and third trochanters are well developed. The nutrient foramen is ap-
proximately halfway down the shaft, which is oval in cross-section.
The medial epicondyle is well developed. The distal trochlea is
assymetrical and relatively deep. The medial condyle is larger than the
lateral condyle. UF 7256 shows an additional thickening of spongy
bone on the medial condyle (this is also developed in some UF
specimens of Equus), whereas the three other specimens, UF 7432,
7436, and 7435 have no bony thickening.
 The astragalus (UF 21323) is too water-worn to be described here.
 The navicular (Fig. 12, Table 8) is represented by UF 21324 (right),
UF 10697 (left), and UF 21322 (left). Hussain (1975) noted a trend in
the evolution of the equid navicular for the transverse width to become
greater than the anteroposterior length. This feature is clearly related
to its increased importance in transmitting weight to the medial (III)
metatarsal. Hussain's navicularr diameter/width index" (ratio X 10)

TABLE 7.-MEASUREMENTS OF FEMORA FOR Nannippus phlegon FROM FLORIDA.
 AP length' Transverse3 Transverse5
 proximal width prox. AP length4 width
 articular articular distal distal
Specimen Length' surface surface trochlea trochlea
UF 7436, Right 59.0 46.6
UF 7256, Left 272.5 53.2 79.4 73.3 64.1
UF 7432, Left 66.9 56.2*
UF 7435, Left 68.1
Proximal tip of greater trochanter to distal-most part of medial ridge.
'Distance between dorsal-most and plantar-most points of greater trochanter.
'Medial-most point on head and lateral-most point of greater trochanter.
'Dorsal-most and plantar-most points on medial condyle.
'Medial-most point on medial epicondyle to lateral-most point on lateral epicondyle.
*Measurement approximate.


Vol. 25, No. 1