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  Section: Anatomy of Vertebrate Animals » The Classification and Organization of the Mammalia
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The Toxodontia


This order has been founded for the reception of the large extinct Mammal (Toxodon), remains 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.


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