Hapalidæ. The Hapalidæ or Marmosets are no larger than squirrels, being the smallest monkeys. They are found mostly in Brazil.
There is a broad septum between the nostrils. Their dentition is 2/2 1/1 3/3 2/2, and is distinctive, for the remaining Anthropoidea have 3/3 molars. The tail is long, hairy, and non-prehensile. The arms are not longer than the legs. The thumb (pollex) is long, but is not opposable. All the digits except the great toe (hallux), which is small, have curved, pointed claws. There is no bony external auditory meatus. There are no cheek pouches, or ischial callosities. The Hapalidæ often bear three young ones at a birth, whereas the other Anthropoidea commonly bear but one. There are two genera of Marmosets, viz.: Midas and Hapale.
Cebidæ. The Cebidæ are most at home in Brazil. They have a broad septum between the nostrils. Many of them have prehensile tails. The dental formula is 2/2 1/1 3/3 3/3, and is characteristic. There is no bony external auditory meatus. There are no cheek pouches, or ischial callosities. All the digits are provided with flat nails. The thumb (pollex) is not opposable.
This family includes the following genera, viz.: Tee Tees (Callithrix), Howling Monkeys (Mycetes), Spider Monkeys (Ateles), Squirrel Monkeys (Chrysothrix), and Capuchin Monkeys (Cebus).
Cercopithecidæ. This family includes the Old-World dog-like Apes. They are quadrupeds, and the muzzle or snout is quite dog-like. There is a narrow septum between the nostrils. The dental formula is 2/2 1/1 2/2 3/3. The sternum is narrow. The tail is not prehensile. The cæcum has no appendix vermiformis. There is a bony external auditory meatus. There may or may not be cheek pouches. Over the rough surface of the everted ischia the skin forms callosities (ischial callosities) which are often brightly colored. The thumb (pollex), when present, is opposable. This family includes two genera, Macaques (Macacus) and Baboons (Cynocephalus).
Simiidæ. This family includes the Anthropoid Apes of the Old World. They are less quadrupeds than the former, often walking in a semi-erect position. The dental formula is 2/2 1/1 2/2 3/3. The sternum is broad. The cæcum has an appendix vermiformis. The nasal septum is narrow. The pectoral limbs are much longer than the pelvic ones. There is a bony external auditory meatus. There are no cheek pouches. Only in the Gibbons are there ischial callosities, in whom they are small. The thumb (pollex) is opposable. No visible tail. This family includes the following genera, viz.: Chimpanzees (Anthropopithecus), Gorillas (Gorilla), Orangs (Simia), and the Gibbons (Hylobates).
Hominidæ. This family of Anthropoidea includes only the human species (Homo sapiens). The dental formula is 2/2 1/1 2/2 3/3. The tail is not visible. The Hominidæ differ from the Simiidæ, structurally, mainly in the more perfect assumption of the erect attitude. There is a more complete adaptation of the pelvic limbs to bearing the weight of the body, correlated with compensating alteration in the curvature of the spinal column. The big toe (hallux) is not opposable, and also it is often longer, never shorter than the other toes, and is not abducted from them. He has a far better heel than the Simiidæ. The thumb is far more opposable in man. There is a greater length of the pelvic limbs compared with the pectoral limbs. The canine teeth are much smaller and do not project beyond the level of the others. The brain has a much greater size and complexity. Man has a larger forehead, smaller cheek bones, smaller supraorbital ridges, a less protrusive face, and a true, well-marked chin.
The Simiidæ are subdivided into the two following groups, viz.:
- Sub-family 1.—Hylobatinæ.
- Genus 1.—Hylobates (Gibbons).
- Sub-family 2.—Simiinæ.
- Genus 1.—Simia (Orangs).
- Genus 2.—Gorilla (Gorillas).
- Genus 3.—Anthropopithecus (Chimpanzees).