A Hand-book to the Primates, Volume 1 (of 2)

by Henry O. Forbes

GENUS MICROSYOPS.

Microsyops, Leidy, Proc. Acad. Nat. Sci., Philad., 1872, p. 20.

Limnotherium, Marsh, Amer. Journ. Sci., 1871, ii., p. 43 (in part).

This genus is easily distinguished, as Cope points out in his sumptuously illustrated "Vertebrata of the Tertiary Formations of the West," by the absence of the first (anterior) inferior pre-molar, and probably of the superior first pre-molar also. The canine tooth of the lower jaw is very large. The posterior pre-molar has an internal cusp, and the molars two front inner cusps. There are three species, distinguished chiefly by size, M. spierianus (Cope), very small; M. elegans (Marsh), the largest, with seven teeth succeeding the canine in the lower jaw; and M. scottianus (Cope); all from the Eocene of Wyoming.

GENUS HYOPSODUS.

Hyopsodus, Leidy, Proc. Acad. Nat. Sci., Philad., 1870, p. 109.

The present genus is recognised by the front inner cusp of the lower molars being single, and their heel presenting a cusp at its inner hind angle (except in H. acolytus). Of the upper pre-molars, the median and posterior have an internal cusp; and the molars have two outer and two inner cusps with two small intermediate tubercles. There are six species known, from the Wasatch and Bridger beds of Wyoming and New Mexico, of which H. acolytus is distinguished by having the heel of the anterior and median lower molars without an inner hind cusp. Professor Cope remarks that though the species of this genus are not numerous, individuals of some of them are exceedingly common in the Eocene beds of Wyoming. H. paulus and H. minusculus, Leidy, H. vicarius and H. powellianus, Cope, with H. jurensis, Rutimeyer, from the Upper Eocene of Egerkingen, are the best known species.

The genera Indrodon, Cope, from the Lower Eocene Puerco formation of New Mexico, with three cusped upper and four cusped lower molars; Opisthotomus, Apheliscus, and Sarcolemur, Cope, from the Wasatch of Wyoming; Hipposyus, Leidy; Bathrodon, Mesacodon, and Stenacodon, Marsh, from the Middle Eocene Bridger beds; are of doubtful affinities.

II. THE MONKEYS AND APES—SUB-ORDER ANTHROPOIDEA.

This Sub-order, though containing animals of much higher organisation than the Lemuroidea, embraces species presenting many different grades of intelligence, and ranging in size from the Pigmy Marmoset, not larger than a small Kitten, to the ponderous Gorilla and the genus Homo. In external characters the Monkeys and Apes have in general a shorter and less Dog-like nose than the Lemurs, thin lips and a more distinct face; while their eyes, situated on the face, are invariably directed forwards, and never outwards, or to the side. The opening of their nostrils is either outward (as in those inhabiting the New World), or downwards (as in the bulk of the Old World species). All of them are covered with hair; the tail may be long, short, or wanting. The proportions of the fore-limbs to the hind- vary much in the different groups. The great toe, as well as the thumb, is (except in a few species) fully opposable, so that in the majority of members of the Sub-order, the foot is as good a prehensile organ as the hand. From this circumstance comes the designation, Quadrumana, or "four-handed," so often applied to these animals. In a few species the thumb is rudimentary or absent, but the fore-finger, the absence of which characterised some of the Lemurs, is always present and well developed, and the corresponding digit in the foot (except in the Marmosets) has a flat nail instead of a claw. The mammæ of the Anthropoidea are always situated on the breast. If we examine the structures underlying the skin, we find that in the skull the orbits are entirely shut in by a bony wall, so that the finger cannot be passed into the temporal depression behind, as could be done in the Lemurine skull, and that the lachrymal foramen opens within the cavity for the eye. In the present Sub-order there is no toothless space in the mid-line of the upper jaw, the incisor teeth being set close together; but there is always a vacuity, except in Man, between the incisors and the canine tooth. The lower canine teeth do not resemble in form the incisors, nor do they protrude horizontally, as in the Lemurs. The two halves of the lower jaw are always co-ossified together, when the animal is full grown. The humerus, or arm-bone, never has an entepicondylar foramen on the inner side of its lower portion, and the bones of the fore-arm (the ulna and radius) are never ossified together, nor are those of the lower leg (the tibia and fibula); so that there is perfect freedom for every movement necessary for grasping and walking, or for rotating the hand or foot on the wrist and ankle.