BULLETIN FLORIDA STATE MUSEUM


two-thirds to three-quarters of the way down the volar side of the
metacarpal.
 On the shaft, just proximal to the distal trochlea, are prominences
mediallyy and laterally) for the attachment of the superficial collateral
ligaments. Sondaar (1968) noted that these prominences are more dor-
sal in Hipparion than in, for example, Anchitherium or Pliohippus,
where they are more centrally located on the medial and lateral sur-
faces of the metacarpal. In relatively primitive horses such as Parahip-
pus, a depression just proximal to the dorsal surface of the distal
trochlea accommodates the first medial (III) phalanx. Sondaar
(1968:30-31) stated that this depression: "gives the proximal [first
medial] phalanx more freedom when the fetlock joint is flexed." This
depression is reduced or absent in advanced horses such as Equus. In
Florida N. phlegon this depression is very poorly developed relative to,
for example, Parahippus. The distal trochlea is bilaterally symmetrical
with a strong sagittal ridge. This distal ridge is very well developed in
Florida N. phlegon, as in other more advanced horses. Also, the distal
ridge increases in circumference in more advanced horses; it extends
about 180 in Parahippus whereas it spans about 2200 in Equus (Son-
daar 1968). In the two UF specimens this distal ridge extends from
roughly 2400 to 2650 around the trochlea (Table 6). Apparently this
distal ridge was most progressively developed in N. phlegon, but this
should be confirmed by more than the two specimens available in the
present study.
 Sondaar (1968) noted that the ratio of width of the deep collateral
ligament prominences to the width of the distal trochlea is greater
than 1 in relatively primitive horses and less than 1 in relatively ad-
vanced horses. This ratio is close to 1 (.95 and 1.02) for the two UF
specimens of Florida N. phlegon.
 The right and left lateral (IV) metacarpals are represented by UF
22637 and UF 22636 (Fig. 10). Proximally there is an articular facet for
the uniform and two articular facets for the medial (III) metacarpal.
It is difficult to determine from these specimens whether or not
metacarpal V was present. The shaft is three-sided, relatively slender,
and tapered. On its medial surface are rugose areas for attachment
with the interosseus metacarpal ligaments. The distal trochlea for ar-
ticulation with the lateral phalanges is not preserved (see discussion of
distal lateral metapodials below).
 The left lateral (II) metacarpals are represented by UF 22635 and
UF 21326 (Fig. 10). Proximally there is a triangular-shaped facet for
articulation with the trapezoideum. Proximodorsally are two small
facets for articulation with the medial (III) metacarpal and the
magnum. The proximovolar area, which is well preserved, has no ar-


Vol. 25, No. 1