This order has been founded for the
reception of the large extinct Mammal (Toxodon
of which have been discovered in the later tertiary deposits
of South America.
The supraoccipital surface of the massive skull slopes
obliquely upward and forward. There are supraorbital prolongations.
The zygomata are very strong and arched, and
the bony palate is very long.
In the upper jaw there are two small, inner, and two large,
outer, incisors. In the lower jaw there are six incisors. In
the mandible there are canines in the middle of the interval
between the incisors and the grinders. In the upper jaw of
the adult, only indications of the former existence of alveoli
for canines remain. The grinding teeth are seven on each side
above, and six on each side below. They are greatly bowed
(whence the name of the genus), so as to be convex outward
and concave inward. They grow from persistent pulps, and
the enamel is absent upon their inner faces.
The centra of the cervical vertebrae have flattened articular
faces. The dorso-lumbar vertebrae and the sacrum are not
known. The ribs are spongy internally, like those of ordinary
Mammals, not compact, as in the Sirenia.
The scapula has a very large supraspinous fossa, as in Tapirus
. There is no acromion, and the coronoid is very
small. The humerus and the ulna are very massive, but the
rest of the fore-limb is unknown. The femur is devoid of any
third trochanter, and, like the tibia and astragalus, presents a
good many points of resemblance to the corresponding bone
in the Elephants.
It is a curious comment upon the pretension to reconstruct
animals from mere fragments of their bones and teeth which
some have put forward, that, although we know the skull, the
dentition, and the most important of the limb-bones of Toxodon
no one ventures to predict the characters of its feet, still
less to say any thing about its internal organization. Even its
zoological affinities are extremely doubtful, and it is hard to
say whether Toxodon
is merely an aberrant Ungulate, or
whether it is the type of a new order.