Chapter M

Length of first phalanx ·022
Width of first phalanx ·012
Length of second phalanx ·013
Width of second phalanx ·010
Length of ungual phalanx ·005
Width of ungual phalanx ·010

PALÆOSYOPS, Leidy.

Hayden's Geological Survey of Montana, 1871.--Proceedings
Academy Natural Sciences, Philadelphia, 1871, p.
118.--_Limnohyus._--Marsh, American Journal Science and Arts,
1872, p. 124.

_Generic characters._--The dentition is full, I. 3, C. 1, Pm. 4, M. 3; the same in lower jaw. The internal cones of the superior molars isolated from the crescentoid crests. One inner tubercle on the last three premolars. One internal cone on the last superior molar. In lower jaw, true molars with four acute tubercles alternating in pairs and connected by oblique crests. The last molar adds a fifth posterior tubercle. The last premolar lacks the posterior inner tubercle. The canines are in continuity with the incisors.

A broad, triangular forehead. A wide zygoma. Long, projecting nasals. Large temporal fossæ. High sagittal crest. Prominent and nearly vertical occiput.

Palæosyops major, Leidy.

Survey of Wyoming, 1871, p. 359.--_Limnohyus robustus._--Marsh,
American Journal Science and Arts, 1872, p. 124.

_Specific characters._--Sagittal crest short and thick. Temporal fossæ not very deep. Frontals diverge rapidly. Occipital condyles wide and low; the same is true of the foramen magnum. Meatus auditorius high and deep. Glenoid cavity shallow; no internal process. As compared with _P. Paludosus_, post-glenoid process not so much compressed. Occipital region comparatively higher and not so concave. The occipital condyles are more prominent. The zygomas are lighter. Head larger than _Paludosus_, perhaps not so large as _Vallidens_.

Description from (i) a head, complete, but distorted, with complete dentition, upper and lower. (2) A head somewhat crushed, and lacking some portions, with full set of upper molars and canines. (3) A great number of fragmentary specimens of different parts of the body.

_Dentition._--In the upper jaw the incisors are arranged in a semi-circle as in _P. paludosus_; they have long fangs and short, conical crowns, with a decided basal ridge, which is very strong in the third. They increase from first to third, which is very large and pointed.

The canines have very large and long fangs (longer than the crowns). The crowns are very stout and pointed, constituting formidable weapons. In section they are nearly circular, with a distinct hinder margin and a slight recurve. A rudimentary anterior margin is sometimes present, and of the faces thus marked off, the inner is much smaller and flatter. The general direction is forwards, downwards, and slightly outwards. There is a diastema of about half an inch between the incisors and canines.

_Premolars._--The first is very small, about half an inch from the canine, simple and conical, with an obscurely marked basal ridge, and two heavy fangs.

Further description of the upper dentition is unnecessary, owing to the complete work of Dr. Leidy upon the subject.

The _lower incisors_ are placed in a semi-circular row, and are somewhat procumbent, though hardly as much so as in the tapir. They are much as in _P. paludosus_, but are relatively smaller, and have not such distinct basal ridges; features which indicate a departure from the carnivorous type, and a nearer approach to the herbivorous type. The lateral incisor, though the largest of the series, is not so large nor so pointed as in _P. paludosus_. There is no diastema.

The _canines_ are about equal in size to those of the upper jaw, growing from stout fangs and permanent pulps. The margins of the crowns are more decided, and are smooth, leaving a very narrow and flat inner face. A feeble basal ridge. When the jaw was closed, the lower canines passed inside and in front of the upper.

The _first premolar_ stands immediately behind the canine, is longer than that of the upper jaw, consisting of a single pointed lobe implanted by one fang, slightly recurved with a flat inner and convex outer face. Passing in front of the first upper premolar, it leaves a considerable diastema between this and the second premolar.

The _mandible_ approximates in form that of the tapir; the lower border is less curved fore and aft, the alveolar border is slightly concave antero-posteriorly. The molars converge in front, presenting a very different arrangement from that in _Sus_. The ramus is heavy, contracting in depth forward, and very slightly in section. Below the alveolus, on the interior side, the ramus is greatly swollen for two thirds of its depth, to accommodate the very long and strong molar fangs.

The rami converge to the second premolar, where they expand laterally to the canine alveolus. The symphysis is shorter relatively than in _P. paludosus_, and the chin is regularly rounded in front. The mental foramen is below the second premolar. The dental foramen is small, very high up, and far behind the molars. The alveolar border ascends rapidly behind the last molar, expanding laterally into two ridges.

The coronoid is slender and recurved. The condyle is broad, flat behind, inclines forward internally; there is scarcely any depression between the condyle and the coronoid. The masseteric fossa is very wide and deep. The angle of the ramus is broken, but evidently has no such posterior extension as in _P. paludosus_. It thins out rapidly behind.

_Measurements._

--------------------------------------------------+---------+----------
| P. pal. | P. major.
+---------+----------
UPPER JAW. | M. | M.
Length of entire molar series | ·147 | ·170
Length of three true molars | ·085 | ·102
Length of three premolars | ·058 | ·068
Diameter of last molar, transverse | ·039 | ·047
Diameter of last molar, antero-posterior | ·036 | ·036
Diameter of second molar, transverse | ·036 | ·040
Diameter of second molar, antero-posterior | ·033 | ·036
Length of incisor series | ···· | ·075
Fore-and-aft diameter of canine at base | ·016 | ·021
Length of crown of canine | ···· | ·033
Diastema between canines and incisors | ···· | ·013
Diastema between canines and molars | ···· | ·010
--------------------------------------------------+---------+----------

---------------------------------------------------+---------+----------
| P. pal. | P. major.
+---------+----------
LOWER JAW. | M. | M.
Incisor series | ···· | ·073
Median incisor fang, length | ···· | ·034
Median incisor crown, length | ···· | ·012
Diameter of median incisor crown, transverse | ···· | ·009
Diameter of lateral incisor crown, transverse | ···· | ·011
Diameter of lateral incisor crown, antero-posterior| ···· | ·012
Length of fang of canine | ·055 | ·052
Extreme breadth of fang of canine | ·023 | ·024
Crown of canine, length | ···· | ·034
Crown of canine, fore-and-aft diameter at base | ·019 | ·021
Diameter of first premolar, antero-posterior | ·015 | ·010
Diameter of first premolar, transverse | ·009 | ·007
Diastema between first and second premolars | ···· | ·014
Length of entire molar series | ·164 | ·186
Length of molar series, omitting first premolar | ·132 | ·163
Diameter of last molar, antero-posterior | ·017 | ·050
Diameter of last molar, transverse | ···· | ·027
Depth of jaw below last molar | ·068 | ·075
---------------------------------------------------+---------+----------

Among other specimens obtained at the divide between Henry's Fork and Cottonwood Creek, was a nearly complete but somewhat shattered skeleton of a _Palæosyops major_, found contiguous to the head of the same, parts of which are just described. Portions of these are figured on a one fourth scale in Plate II. The description is from a nearly perfect atlas and axis, several cervical, dorsal, and lumbar vertebræ, more or less complete, and a portion of the sacrum and pelvis, in addition to several bones of the limbs.

The _atlas_ has a broad inferior arch, contracted antero-posteriorly, and deeply notched for the prominent odontoid of the axis. The heavy superior arch, inclosing a large and depressed neural canal, is capped by a low tuberosity. It slopes into a flat, and very broad transverse process, which thickens backwards, and is perforated by the vertebraterial canal. Forwards the transverse process is notched for the exit of the first spinal nerve. The anterior or condylar faces are continuous, deeply concave from above downwards; and slightly so from side to side; while the posterior faces are oval, nearly flat, and directed backwards and inwards.

The _axis_ is proportionately small, with a long opisthocœlous centrum, depressed, and produced forwards into a stout conical odontoid process, and marked below by a strong hypapophysial keel, which, developed on the latter half, thickens backwards. The wide and thin pedicles inclose a high neural canal, support the posterior zygapophyses and a prominent and peculiar neural spine. The latter is flattened, broad, and recurved posteriorly, thinning rapidly forwards into a prow-shaped recurved edge. The transverse processes arising from the latter half of the centrum are undersized and widely perforated at base. The anterior faces are very broad, directed outwards, and slightly rounded from above downwards; they expand as they diverge (see Fig. 2). The post-zygapophyses are small convex faces, projecting at the base of the neural spine.

The _remaining cervicals_, five in number, are short, all carinate, except the seventh, and opisthocœlous; with the faces expanding only slightly beyond the body of the centrum. A peculiar feature is a small pit upon the convex anterior face, indicating either a ligamentous attachment with the antecedent vertebra, or a remnant of the notochord. This is a feature we have not noticed elsewhere. A long and heavy transverse process supports a large and widely-perforated inferior lamella. The pedicles are quite wide at base, inclosing a large neural canal. The entire upper part of the arch is unfortunately wanting.

The dorsal centra are smaller than the cervical, slightly opisthocœlous, and carinate. They are sub-cylindrical anteriorly, with decided costal surfaces before and behind; approaching the lumbar region they become subtriangular. A high neural arch supports a stout, but never very high neural spine; this projects backwards, keeled in front, expanding and deeply grooved behind. The zygapophyses are small and nearly vertical. There is a short and thick transverse process.

The _lumbar_ vertebræ are long, decidedly opisthocœlous, becoming wider and more depressed as they approach the sacrum. The first _sacral_ vertebra presents the same characteristics as the last lumbar, only the body of the centrum is slightly shorter. It has a very broad pleuropophysial plate. The remaining sacral vertebræ are broad, and very greatly depressed, rapidly decreasing in size. The transverse processes are slender. The very low neural spines anchylose into a long ridge. The number cannot be ascertained, owing to the fragmentary state of the sacrum. The caudals indicate a tail of not very great length; as the neural canal is small and persists in only a few of the anterior vertebræ.

_Measurements of Vertebræ._ _Pal, major._