Chapter M

Length of molar series ·148
Length of premolar series ·062
Length of true molar series ·089
Fore-and-aft diameter of second premolar ·022
Transverse diameter of second premolar ·023
Fore-and-aft diameter of third premolar ·022
Transverse diameter of third premolar ·023
Fore-and-aft diameter of first molar ·023
Transverse diameter of first molar ·026
Fore-and-aft diameter of second molar ·028
Transverse diameter of second molar ·031
Fore-and-aft diameter of third molar ·039
Transverse diameter of third molar ·044
Distance between last molars ·058
Distance between first premolars ·049
Distance between first molars ·074
Fore-and-aft diameter of root of canine ·060
Transverse diameter of root of canine ·039
Length of diastema ·072
Distance between canine alveoli ·080

_Lower Jaw._--Dr. Leidy has very kindly sent us some of the lower molars of an undescribed _Uintatherium_, which may belong to this species. They consist of the anterior lobe of the last molar, and second and third premolars entire. They all have nearly the same conformation, consisting of three acute pyramidal lobes, of which the anterior is very much the highest and broadest; the median lobe is partly separated from the anterior by a valley which opens outwards, while the valley between the posterior and median lobes passes completely across the tooth. The highest point of the crown is the inner end of the anterior lobe; but the difference between this and the outer end, very great in the molars, becomes slight in the premolars. The inner end has an accessory tubercle just at the lip of the anterior lobe, and there is another on the anterior basal ridge. This latter feature would seem to distinguish it from _U. robustum_.

The basal ridge is distinct in front and behind, indistinct on the external side, and entirely absent from the internal.

_Measurements._

(TEETH, LOWER JAW.)
M.
Transverse diameter of last molar ·026
Height of highest point above cingulum of last molar ·023
Fore-and-aft diameter of second molar ·0285
Transverse diameter of second molar ·023
Height of second molar ·0215
Length of fourth premolar ·021
Width of fourth premolar ·015
Height of fourth premolar ·020
Length of third premolar ·020
Width of third premolar ·015
Height of third premolar ·014

_Vertebræ._

_Cervical region_ (Plate VI., Fig. 1).--(Only one preserved, probably fifth or sixth.)

The centrum is short, compared with the dorsals, but is much longer than the cervical centra of the _Proboscidea_; it is broad and depressed, oval in form, and slightly opisthocœlous. The zygapophyses are developed upon tuberous projections of the pedicles; they are large, flat, and in the same plane with each other. The diapophyses are very slender and short, and but slightly heavier than the parapophyses, with which they unite, enclosing a large vertebraterial canal. At the anterior margin of the parapophysis, a small pointed process projects downward.

The pedicles are low and very heavy, bounding a narrow neural canal.

The epiphyses are not so completely ossified as they are in the dorsal region.

_Dorso-lumbar region_ (Plate VI., Figs. 2, 3, 4, 5),--(Description based upon nine dorsals and two lumbar vertebræ.)

The centra are large, subtriangular, and slightly compressed; they are opisthocœlous, but less so than in the _Proboscidea_. They increase in size slowly but regularly from before backwards. In the middle dorsal region they are excessively expanded laterally for the posterior-costal attachments; but become less broad and higher as they recede in the series. In the middle of the series the centra are marked by a prominent hypophysial keel.

In the anterior dorsals the costal surfaces are developed almost entirely upon the pedicles, and are two in number. These are very large in about the sixth and seventh, and meet. They decrease in size as they recede. In the middle region the posterior costal surfaces are small, lozenge-shaped facets, and are developed upon thin lateral projections of the centra.

The centrum of the last dorsal is heavy, resembling the centra of the lumbar, from which it is distinguished by a single pair of small costal surfaces, developed, half on the pedicles and half on the centrum.

The neural spines are markedly smaller than those of the _Proboscidea_ and _Rhinoceros_; in the anterior part of the dorsal region the spines have the same angle as the corresponding ones in _Mastodon_. The spines of the twelfth and thirteenth (approximately) are much expanded at the ends and bifid; in the last dorsals they are wide, straight, and very thin; in the lumbar region they are short, stout, tuberous, and stand almost at right angles to the axis of the vertebræ. The laminæ in the anterior part of the series are long and thin, decreasing in length but increasing in thickness from before backwards. The zygapophyses in the fore part of the dorsals are mere flat facets on the laminæ; they increase in size and become characteristic in the posterior part of the dorsal region. The pre-zygapophyses of the last lumbar vertebra are very large, deeply concave, and parallel with the axis of the column. The metapophyses appear in the middle of the series, and regularly increase in size to the last lumbar. From their appearance the pre-zygapophyses are developed upon them.

The transverse processes present the most unique feature of the vertebral column. In the anterior region they are long, wide, and rugose, and in the same plane with the laminæ; they send directly out wide, downward-curving projections. In the middle dorsal region the transverse processes lose these thin projections, and become heavy and subtrihedral, with a smooth facet on their lower face for articulation with the tubercle of the rib; their upper face is here a little twisted from the plane of the laminæ. In the posterior dorsal region the transverse processes lose the facet for the articulation with the tubercle of the rib, and become short and very thin, pointing slightly backwards.

The lumbar transverse differ from those of the last dorsal in having a median transverse ridge on their posterior face, and are directed more vertically out.

The pedicles throughout most of the dorsal series are short, heavy, and deeply notched behind. In the posterior dorsal region they become longer and more slender, resembling almost exactly the pedicles of the lumbar region.

_Sacral region._--The sacrum is composed of four vertebræ, three true and one pseudo-sacral. The centra are extremely depressed, and rapidly decrease in width and thickness from before backwards. The first is shorter than the last lumbar, but much longer than the other sacrals, which are subequal.

The face of the first is elliptical, and is nearly three times the diameter of the fourth, longitudinally. The metapophyses are exceedingly large and tuberous on the first; with wide, deeply concave pre-zygapophyses developed upon them; in the other three the metapophyses are rudimentary.

The transverse processes are long and wide in the first three; widest in the first but thickest in the second; long and thin in the fourth. The pleuropophysial segments of the true sacrals are very heavy.

The foramina enclosed by the transverse processes are large; and have, on the internal side, their long diameter obliquely transverse to the axis of the sacrum.

The inferior faces of the centra are slightly concave in the first three. The first and fourth have slight hypophysial keels.

The neural canal is very wide and depressed in the first, but decreases rapidly backwards, becoming extremely small in the last.

_Caudal region_ (Plate VI., Fig. 6).--(Description based upon the first four.)

The centra of the caudal vertebræ are rather long, narrow, and greatly depressed in the middle; they decrease in size gradually backward. The pedicles and laminæ are short and thin, enclosing a small neural canal. The neural spines point directly back, being almost parallel with the axis of the centrum. They are slender and tuberous at the extremity. The transverse processes are very long, wide, and thin, thickened somewhat at the ends, and project directly out; they decrease in size backwards. From the persistence of the neural canal, and from its comparative size, it would seem as if the tail was considerably larger than that of the elephant.

_Measurements of Vertebræ._

_Cervical region_ (Plate VI., Fig. 11).

M.
Diameter of cervical (vertical) ·079
Diameter of cervical (transverse) ·111
Diameter of cervical (fore-and-aft) ·051
Extreme length of prolongation of pedicles for
zygapophyses ·089
Long diameter of vertebraterial canal ·040
Width of pedicles ·035

_Dorsal region_ (Plate VI., Figs. 2 and 3).