NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN ']']

as in

Meniscotherium

but is comparatively straight

and

not nearly so slender.

The

Tetraclaenodon first metatarsal, however, is relatively longer, being nearly tv^o-thirds the length of the second,

and

only a

little

more

slender.

The

shaft is

somewhat bowed

as in

Menisco-

therium.

The

base or proximal extremity, it is further noted, exhib-

its a short ventrolateral spur, unlike Meniscotherium,

and

the artic- ularsurfacefor theinternal

cuneiform

isonlyslightlyconvex.

MetatarsalII.

— The

second metatarsal of

Meniscotherium

is inter- mediateinlength

between

the third

and

fourth,but its distalextremity

is about even withthat of the fourth in the articulated foot, because of the

more

proximal position of the base of the second metatarsal.

The

proximal surface forthemiddle

cuneiform

isnearly triangularin outline, dorsoventrally elongate

and

slightly convex. Transversely the facet is distinctly concave.

The

medial surface of the base is

somewhat roughened and

a short distance distally exhibits a

low

knob. Apparently, however, there is

no

^faceting for either the inter- nal

cuneiform

or the first metatarsal.

The

lateral surface of the base, however,

shows

a slightly concave facet proximodorsally

and

asmallerflattened facetproximoventrally for the externalcuneiform.

More

distally, the lateral surface

conforms

to the medial surface of the third metatarsal base, but ^I find

no

evidenceof articular contact.

The

shaft maintains a width at least as great as the base,

becoming

little wider distally,

and

is relatively

compressed

dorsoventrally. It is essentially straight but

may

be slightly

bowed

dorsally in

some

individuals.

The

convexity of the transversely

wider

distal extremity

is slightly oblique

and shows

a

pronounced median

keel only

on

the ventral surface.

Except

for its

more

flattened proximal extremity for articulation with the middle

cuneiform and

relatively wider distal extremity, the second metatarsal in

Phenacodus

appears very

much

like that in Meniscotherium.

That

in Tetraclaenodon is

more

elongate

and

relatively slender.

The

proximal surface of the base, like that in

Phenacodus,

is flattened although the outline is similar to that in Meniscotherium.

The

^distal extremity is broad in

comparison

with thewidth of the base, buttheseare small relativetothe length of the shaft.

Metatarsal III.

— ^The Meniscotherium

third metatarsal averages about 5 or

6

percent longer thanthe second.

The

shaft is broad

and

flat, increasing

somewhat

in width distally.

The

proximal extremity

shows

the asymmetric

T-shaped

base so frequently encountered in the

mammalian

thirdmetatarsals. This surface forthe external cunei-

NO. 2

A STUDY OF MENISCOTHERIUM — GAZIN 79 form

is gently

convex

dorsoventrally, slightly oblique transversely,

and markedly

constricted ventral to the broad

and

dorsally

convex

superior margin.

The

constriction is greatest

on

the lateral side,

and

ventral to this the ventrolateral

margin

of the surface for the middle

cuneiform may

be slightly deflected proximally.

Adjacent

to this there is

a

small flattened facet

on

the lateral surface for the ventral portion of the fourth metatarsal base. Dorsal to this facet

on

the lateral sideof the third metatarsal there is a deeply concave, ventro- laterally facingsurface for articulation with a medial

knob

orpromi- nenceclose to the proximal extremity of the fourth metatarsal.

The

medial surface of the base of the third metatarsal

shows a

distinct knob, proximodorsally,that fits intoa depression distal to the dorsal facet forthe external

cuneiform on

the baseof thesecondmetatarsal.

The

convexity of the relatively

broad

distal extremity has

an

axis at right angles to that of the shaft

and

exhibits a

prominent

keel ventrally.

The

similar appearing

Phenacodus

third metatarsal, as the second, has a generally flatter proximal surface for the external

cuneiform and

a relatively broader distal extremity. It should be noted,

how-

ever, that the proportions of the metatarsals as outlined here apply

more

particularlyto

comparison

with

Phenacodus primaevus

material, as the

Phenacodus

copei metatarsals are relatively elongate

and

slender,

somewhat more

as describedforTetraclaenodon.

Metatarsal IV.

— ^The Meniscotherium

fourth metatarsal is a trifle shorter than the second,

and somewhat more

so than the third, as noted above.

The

shaft is dorsoventrally

compressed

but

more

slen- der than that of the third

and

has a slight lateral curvature so that the distal extremities tendto diverge.

The proximal

surface for the cuboid^isdorsoventrally

and

transversely

convex

overitsbroader dor- sal portion, but the narrower, ventromedially directed part is notice- ably deflected proximally, so that the ventral

margin

of the base extends into the deeply impressed peroneal groove of the cuboid.

Adjacent

to the recurved ^ventral portion of the cuboid surface,

on

the medial side of the fourth metatarsal, is a facet for the third metatarsal.

A prominent knob on

the medial side of the base, just distal to the dorsomedial

margin

of the cuboid facet, is convexly faceted for the concavity

on

the lateral side of the third metatarsal base.

The

lateral side of the fourth metatarsal base is also deeply concave

and

exhibits a distolaterally

and somewhat

ventrally facing concave facet for the fifth metatarsal.

The

convexity

on

the distal

extremity of the fourth metatarsal is

narrower

^laterally

and

its axis

isslightlyoblique,

more

^distal

on

themedial side.

Differences

from

the

Phenacodus and

Tetraclaenodon fourth meta- tarsal are essentially those noted with regard to the second

and

third metatarsals, but it

may

be noted that the ventral portion of the cuboid facet is not nearly so recurved, so that in these

forms

the base of the fourth metatarsal does not extend so noticeably into the peronealgroove.

Metatarsal V.

— ^The

^{fifth metatarsal of}

Meniscotherium

is a ^little