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. paludosus. | P. major. | P. 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.