The Arciopithecini

1. The Arctopithecini, or Marmosets, are small, thickly furred, long-tailed, habitually quadrupedal. Squirrel-like animals, which are found only in South America. None of them are provided with cheek-pouches, nor possess bare and callous patches of integument over the ischia. The ears are large and hairy, and the nose is flat and broad as in the Platyrrhini.

The fore-limbs are shorter than the hind-hmbs. The pollex is not opposable, nor susceptible of extensive abduction from the other digits, which it resembles in being provided with a sharp, curved claw. The manus, consequently, is a mere paw, and the term "hand" is not applicable to it. The hallux of the foot is very small, and is provided with a flat nail. The nails of all the other digits of the pes are falcate. The plantar surface is very long, and the digits are very short. It follows from these facts that the term "quadrumarnous" is not applicable, in any sense, to the Marmosets.

The skull is remarkable for the smooth and rounded surface and relatively large size of the brain-case. Although the orbits are large, the brow ridges are inconspicuous, and the occipital region of the skull projects so far backward that the occipital foramen may lie completely upon the under surface of the skull, toward the junction of its middle and posterior thirds; and have its plane almost horizontal, when the face looks forward. The orbit is almost completely shut off from the temporal fossa by bone.

The hyoid resembles that of the Lemurs, its body being narrow and much arched from side to side, while the anterior cornua are strong.

There are usually nineteen dorso-lumbar vertebra, and the transverse processes of the atlas are somewhat broad and flattened.

The dental formula is i. 2.2/2.2 c. 1-1/1-1 p.m. 3.3/3.3 n. 2.2/2.2=32. Thus the number of the teeth is the same as in man and the Catarrhini; but in the number of the premolars and molars the Arctopithecini differ from both the Catarrhini and the Platyrrhini, having one premolar more than the former and one true molar fewer than the latter. In Hapale, the lower incisors are proclivous; and the canines are approximate to them, and similarly inclined, as in the Lemurs.

Although the manus is a paw and the pollex is not opposable, this digit has its proper abductor, adductor, and long and short flexors. The existence of a proper opponens of the pollex is doubtful, but there is an opponens minimi digiti. The flexor longus is completely united with the flexor profundus digitorum, but the tendon for the pollex comes off on the radial side instead of on the ulnar side, as it does in some of the higher Simiadae. The extensor secundi internodii pollicis is united with the extensor indicis, and the extensor minimi digiti gives off slips to the third, fourth, and fifth digits, so that there is a complete set of deep extensors. The four dorsal and three palmar interossei are not distinctly subdivided, but they send slips to the extensor tendons.

There are four perenoei. p. longus, p. brevis, p. quarti, and p. quinti digiti. The flexor brevis dlgitorum of the pes has one division which arises from the calcaneum and goes to the second digit; the other three heads arise from the tendons of the flexor perforans. The flexor accessorius furnishes almost the whole of the long flexor tendons of the hallux, the flexor longus digitorum supplying the perforating tendons of the second and fifth digits; while the flexor hallucis longus gives off the corresponding tendons of the third and fourth digits. The interossei, in the pes, appear to be represented only by the pairs of muscles which act as short flexors of the basal phalanges, and these lie altogether upon the plantar aspect of the five metatarsal bones. The hallux has no special adductor, nor is there any transversus pedis. In fact, the pes is almost as completely a "paw" as is the manus.

The brain has long and relatively large cerebral hemispheres, the posterior lobes of which project far beyond the cerebellum, and thus completely hide it, in the upper view of the brain. The external surfaces of the hemispheres are almost smooth, but the Sylvian fissure is well marked, and there is a trace of that of Rolando. On the inner face of each hemisphere, the calcarine fissure is deep and gives rise to a wellmarked hippocampus minor within the posterior cornu of the lateral ventricle. The corpus callosum has about a third the length of the hemispheres. The septum lucidum is very thick, and the precommissural fibres abundant. The vermis projects beyond the lateral lobes of the cerebellum, and the flocculi are large.