The functional interpretation of this singular diversity of organization in animals otherwise so nearly allied to each other, may not be manifestly apparent to the philosophical zoologist. It was satisfactorily ascertained in the year 1836[1] by the observations of Messrs. Bennett, Owen, Ogilby, and Hodgson, that the suborbital sinus subserved a purpose connected with the generative functions, being dilated and swollen at certain periods of the year. But the connection of the development of the glandular structure of the carneous lacrymal sinus with the degree of ossification to which the cheekbones extend is not obvious. If however we suppose that the large periodical swelling which, according to Mr. Hodgson, forms a huge lump of flesh bigger than, and like in shape to, the yolk of an egg, increases periodically in its dimensions, its backward pressure towards the cheek-bone would be seriously impeded by a bony wall, such as we find in the Tragulus pygmæus or the Auchenia Vicuna. The aponeurotic fascia which fills the lacrymal interspace in the Hyomoschus aquaticus, or the Auchenia Huanaca, would, however, yield more easily, and thus those species would in certain seasons have a greater development of their suborbital sinuses.
Mr. Ogilby[2] laid down the theory "as a general remark, which however he stated was not universal, that in intertropical animals the lacrymal sinus is larger than in more northern species, and in those whose range is limited to mountainous districts." This incomplete induction may be considered partially corroborated by the osteology of the Llamas. In the three varieties, Guanaco, Llama, and Alpaca, a more or less large "sublacrymal lacuna" is left. In the Vicuña, ossification has extended to such a degree as to close this completely up. How does this singular fact bear upon the theory that there is a relation between the gregarious habits of those antelopes and musk-deer which frequent the plains, and the presence of the lacrymal sinuses, and consequent non-ossification of the cheekbones? The species of Auchenia which has no lacuna, is confined to the most elevated table-lands of Bolivia and Northern Chile. The three varieties in which large lacunae are exhibited, are found over the whole Andian range, the Guanaco supporting life alike under the tropical sky of New Granada, or the frozen steppes of Patagonia. In this species we find a large development of the lacrymal interspace. But both the Guanaco and Vicuña are gregarious. It is therefore quite clear that the development of the lacrymal sinus, or the degree to which the lacrymal and other cheek-bones are ossified, have no reference whatever to the gregarious or solitary habits of the species. This was sufficiently proved by the table which was submitted by Professor Owen to the Zoological Society (Proceedings, 1836, p. 36), in which it was conclusively shown that no constancy or correlation existed with respect to the presence or absence of the suborbital sinuses. And the facial interspace seems an equally in-
