OCR Text |
Show 896 SIR V. BROOKE ON THE [Nov. 19, Facts (continued). (8) In some of the Telemetacarpi the distal extremities of the lateral metacarpals is two thirds the length of the metacarpal cannon. In some of the Bovidae (e. g. Gazella), of which family all the species are plesiometacarpal, the proximal extremity of these bones is two thirds the length of the metacarpal cannon. (9) With three exceptions all the Old-world Deer are plesiometacarpal ; and with one exception all the New-world Deer are telemetacarpal. (10) In none of the Old-world Deer is the vomer sufficiently prolonged backwards to divide the nasal cavity into two chambers. In all the New-world Deer the nasal cavity is so divided. (11) The vomer of Megaceros hibernicus exhibits an intermediate condition. The limb in this form is plesiometacarpal, and as highly specialized as in the existing Plesiometacarpi. (12) The Telemetacarpi of the Old World resemble the Plesiometacarpi in the form of their vomer and in the position of the metatarsal tufts. (13) Thirty-three out of the thirty-nine species of Old-world Deer are inhabitants of the Indian or East Palaearctic regions ; and of the eleven subgenera into which they are divisible there is only one (Darna) that has no representative in these regions. Hypothesis (continued). tacarpal and telemetacarpal condition of limbs in existing Cervidae. (9) It is probable that the separation between the upper and lower extremities of the metacarpals took place long after the first Dremotherium-hke Cervidae had found their way into North America. In these the default in ossification began in the upper third of the lateral metacarpals; (12) whilst in the Cervidae remaining in the Old World both modes of reduction obtained a footing, the Plesiometacarpi gaining ultimately the preeminence. (10) The vomer in the early forms of De.er was, as in the existing less-specialized Artiodactyles (e. g. Hippopotamus, Sus, Tragulus), prolonged backwards, dividing the nasal cavity into two distinct chambers. (11) As the competition between rapidly multiplying and allied forms became severe in the Old World, specialization extended to this part of the cranium, and a reduction in the backward extension of the vertical plate of the vomer, and consequent modification of the surrounding parts, set in. It is not improbable that the limbs of the Plesiometacarpi had nearly reached their present stage of specialization before the form of their vomer departed from the primitive type. The Deer of the New World, being less numerous both in individuals and species, and not being subjected to such severe competitions as the Old-world Deer, retained the primitive form of vomer. The greater development of the antlers in the larger majority of Old-world Deer, as compared with those of the New-world Deer, may be |