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Show 1873.] MR. ST. G. MIVART ON THE LEMURS. 507 ones, and that the two groups are no more genetically united to each other than is either one of them to the Carnivora or Cheiroptera. But even if this is not the case, and if both groups really are the descendants of some special but remote common ancestor, nevertheless the number of subdivisions necessary to classify the Artiodactyla is so great as possibly to justify, on that ground, the elevation of that group to the rank of a distinct order. As to the question respecting the zoological value of the Lemuroidea, there can, I think, be no doubt that Man, Apes, and Half-Apes together constitute a group capable of convenient and very distinct zoological definition. The group may be thus defined: Unguiculate claviculate placental mammals, with orbits encircled by bone; three kinds of teeth, at least at one time of life ; brain always with a posterior lobe and calcarine fissure; the innermost digits of at least one pair of extremities opposable ; hallux with aflat nail or none ; a well-developed ccecum; penis pendulous; testes scrotal; always two pectoral mammae. The group thus characterized, is sharply marked off from every other order of Mammals, while its common characters are sufficiently numerous and important to make a coherent whole in spite of the diversity existing between the two subordinal sections into which it is divided. Moreover the number of forms contained in the order is not excessive, nor is the amount of subdivision requisite for classification great. W e may n ow turn to the subdivisions of the order, and seek answers to the three following questions : - 1. What are the characters separating the Lemuroidea from the Anthropoidea! 2. W h a t is the value of the characters which define subordinate groups of Primates'! 3. W h a t is the more prudent course as to the classification of such forms as m a y seem to be probably or possibly distinct in their origin ? The characters which divide the Lemuroidea from the Anthropoidea are as follows:- I. Orbit opening widely into the temporal fossa. 2. Lachrymal foramen on the cheek. 3. Cerebellum much uncovered. 4. Posterior cornu of lateral ventricle very small. 5. Pollex always large. 6. Index of foot with a sharp claw. 7. Posterior cornua of os hyoides shorter than the anterior cornua. 8. Clitoris perforated by the urethra. 9. Uterus two-horned. 10. Placenta bell-shaped, diffuse, and non-deciduate. 11. Allantois very large. The more important of these characters have already been reviewed, and reasons have been advanced tending to show the uncertainty which hangs over them as to the question of their adaptive or genetic nature. With regard to the clitoris, which offers so appparently striking a |
