Natural History of the Mammalia of India and Ceylon

Sub-Order Duplicidentata — Double-Toothed Rodents

These rodents are distinguished by the presence of two small additional incisors behind the upper large ones. At birth there are four such rudimentary incisors, but the outer two are shed, and disappear at a very early age; the remaining two are immediately behind the large middle pair, and their use is doubtful; but, as Dallas remarks, “their presence is however of interest, as indicating the direction in which an alliance with other forms of mammalia more abundantly supplied with teeth is to be sought.”

Dentition of Hare.

Another distinctive characteristic of this sub-order is the formation of the bony palate, which is narrowed to a mere bridge between the alveolar borders, or portions of the upper jaw in which the grinding teeth are inserted.

The following synopsis of the sub-order is given by Mr. Alston:—

“Incisors 4/2; at birth 6/2; the outer upper incisor soon lost; the next pair very small, placed directly behind the large middle pair; their enamel continuous round the tooth, but much thinner behind; skull with the optic foramina confluent, with no true alisphenoid canal; incisive foramina usually confluent; bony palate reduced to a bridge between the alveolar borders; fibula anchylosed to tibia below, and articulating with the calcaneum; testes permanently external; no vescicular glands. Two families.”—‘P. Z. S.’ 1876, p. 97.

There are only two families each of one existing genus—LEPORIDÆ, genus Lepus, the Hare; and LAGOMYIDÆ, genus Lagomys, the Pika, or Mouse-Hare, as Jerdon calls it. There are three fossil genera in the first family, viz. Palæolagus, a fossil hare found in the Miocene of Dacota and Colorado, Panolax from the Pliocene marls of Santa Fe, and Praotherium from Pennsylvanian bone-caves. A fossil Lagomys, genus Titanomys, is found in the Post-Pliocene deposits in various parts of Europe, chiefly in the south.