Chapter M

Astragalus, total width, tibial facets ·048
Astragalus, total length ·056
Astragalus, length, navicular facet ·046
Astragalus, width, navicular facet ·035
Calcaneum, total length ·120
Calcaneum, total breadth ·057
Calcaneum, length of tuber calcis ·050

All the above were found at Henry's Fork Divide. In another locality, in connection with a fine head of _P. major_, was found the lower half of a _humerus_.

The _shaft_ is cylindrical and twisted, expanding widely at the distal end. Of the two condyles the external is the largest; and, to quote from Dr. Leidy, "a deep supra-condylar fossa occupies the front of the humerus, opposed by a deeper and more capacious anconeal fossa." The greatest breadth between the supracondyloid eminences is ·091 m.

Palæosyops paludosus, Leidy.

Cont. to Ext. Vert. Faun, _P. lævidens_ Cope. U. S. Geol. Survey of
Terrs, 1872, p. 591.

_Specific characters._--Second superior molar has but one outer tubercle. The cones are low as compared with _P. major_. The cingula are much less developed. The angle of the lower ramus is much longer. The zygoma is massive and wide. An internal process on the glenoid cavity. Temporal fossæ very deep. Crest of occiput nearly in same vertical line as occipital condyles.

The full details of _P. paludosus_, which follow, may seem somewhat unnecessary, to one familiar with the comprehensive work of Dr. Leidy upon the subject. Care has been taken not to retrace any of his steps; and the descriptions given below are of those parts of the animal which he did not possess at the time of writing. They include (1) a cranium perfect posterior to the orbits; (2) a right _ramus_ mandibuli, with full dentition, except the first premolar; (3) portions of the fore-limbs, scapula, and pelvis, pes and manus, and many fragments of other parts.

Among the first discoveries on Cottonwood Creek, in a stratum of fine green sand, was a head of _P. paludosus_, complete posteriorly, and broken off just behind the orbit. A rear view of this has been admirably figured in Plate I.

_General appearance._--The base of the cranium is of great width; the occiput is high, inclined very slightly backwards, and deeply concave from side to side. The forehead is triangular and narrow. The temporal fossa is of immense size and depth, leaving a small intracranial cavity. The zygomas are heavy, and arching widely outwards give this part of the head a strong resemblance to the _Felidæ_.

_Description in detail._--The narrow but prominent _basioccipital_ segment is broadest posteriorly and tapers forwards; divided by a median ridge, which expands anteriorly into a large tuberosity; a feature also characteristic of the tapir. About half an inch in advance of the condyles are the condylar foramina. The _condyles_ are formed of the exoccipitals, which are low and of great lateral expansion. Their junction with the mastoids is marked by a large foramen. The _par-occipitals_ are short and styliform. The _supra-occipital_ region is very large, high, and deeply concave from side to side, much wider than in the tapir, with a marked interparietal suture. The _condyles_ are wide, but not very deep, approaching each other very closely below. The _basisphenoids_ are long and narrow, tapering forwards. The _alisphenoids_ are mutilated, but indicate large vertical ridges joining the parietals, and heavy pterygoid processes, perforated at the base by the alisphenoid canal. They are again perforated by the foramen ovale three fourths of an inch behind this. This completes the base of the skull.

The _parietals_ are very large, they form nearly the whole of the temporal fossil; which, deep and wide, enclosing a small cranial cavity, contrast strongly with the long and shallow temporal fossæ of the tapir. The parietal crest is very broad, and grooved at the top. This high crest and deep adjacent temporal fossæ we at first mistook as pointing to an exclusively carnivorous type. The forehead has a triangular appearance, from the divergence of the two side ridges of the sagittal crest. The _postorbital_ processes are very large, but do not reach the opposing processes of the _malar_. The orbit is thus left incomplete posteriorly, while in form it greatly resembles that of the _Sus_. The _squamosal_ encroaches considerably upon the temporal; and sends outwards and downwards a great zygomatic process, which arches outwards from the skull as in the _Felidæ_, and is more powerful than in any living carnivore (Leidy.) A strong downward direction is especially characteristic, the whole describing a sigmoid curve. The _mastoids_ are of great size vertically, and transversely they are confluent with the par-occipitals. A low, thick process on the internal side of the glenoid cavity prevents lateral motion.

The _nasals_ are long, broad, and thick, convex from side to side, narrowing slightly anteriorly. They are straight, as in _Sus_, which they resemble more than they do either tapir or rhinoceros. The anterior borders are rounded, and do not reach as far forward as the symphysis of the premaxillary. The _malar_ is broad and thick, probably forming but little of the face, being directed downwards and backwards to meet the zygoma. The postorbital process is short, and rather larger than Dr. Leidy has indicated. The _maxillaries_, smaller proportionately than in _Sus_, form posteriorly the floor of the orbit; while the infraorbital foramen is situated over the last premolar. The premaxillaries fail to reach the nasals.

_Comparative Measurements of Head._

----------------------------------------+----------+---------+-------
| P. | P. |
|paludosus.| major. | Tapir.
----------------------------------------+----------+---------+-------
| M. | M. | M.
Height of occiput | ·122 | ·148 | ·120
Breadth of occiput at post tympanic | | |
processes | ·160 | ·166 | ·110
Breadth of cranium at ends of | | |
post-glenoid processes | ·172 | ·210 | ·126
Transverse diameter of occipital foramen| ·031 | ·049 | ·040
Vertical diameter of occipital foramen | ·027 | ·033 | ·027
Depth of occipital condyles | ·033 | ·039 | ·029
Breadth of occipital condyles | ·040 | ·049 | ·041
Breadth at occipital condyles together | ·082 | ·100 | ·082
Width of basioccipital at anterior | | |
condyloid foramina | ·038 | ·039 | ·028
Width of basioccipital at junction with | | |
basisphenoid | ·025 | ·032 | ·020
Width of crest dividing the temporal | | |
fossæ posteriorly | ·011 | ·020 | ·011
Breadth of cranium outside of zygomata | ·262 | ·280 | ·180
Depth of zygoma | ·046 | ···· | ·036
----------------------------------------+----------+---------+-------

_Lower jaw_ of _P. paludosus_ described from another specimen.

The peculiar feature of this jaw is its remarkable extension back of the molar series (a feature which has not been noticed heretofore), the distance from the last tooth to the angle being greater than the length of the entire molar series. From beneath the last molar, the lower margin curves gently up to the symphysis. The alveolar border is but slightly curved. Behind the last molar the lower margin forms a sigmoid curve, much more decided than in _P. major_ (first upwards and then downwards), and the ramus thins out rapidly to the angle, where it has a slightly raised border; at the diastema the ramus curves outwards so as to throw the canines out of the line of the molars. The symphysis is long.

_Dentition._--The incisors, three in number, from length and shape indicate a semi-circular arrangement, as in most Perissodactyles. They increase from first to third. The crown of the first resembles very much that of the ruminants, but has a straight posterior basal ridge. Its forward edge is worn so as to expose a small tract of dentine. The second is larger, but very much like the first in conformation; while the third has an acute conical crown with a strong basal ridge.

Of the _premolars_ the first is wanting in this specimen. The second is bilobed, the anterior lobe much the larger. It has a small accessory tubercle on its anterior slope. The outer face is rounded, the inner nearly flat. The posterior lobe is very small and obtuse, and with the inner face slightly grooved. In third and fourth the valley between the lobes and the groove on their faces enlarge; while the anterior lobe becomes relatively smaller.

_Measurements of Lower Jaw._