The following are the living orders, viz.: a, Ophidia; b, Lacertilia; c, Chelonia; d, Crocodilia.
Class 7.—Aves. Feathered vertebrata; heart four-chambered; warm-blooded; lungs with accessory air-sacs; bones dense and hollow; jaws encased in horny beaks in modern forms; the fore-limbs form wings; oviparous; eggs are very large and covered by calcareous shell.
- Sub-class 1.—Saururæ: Archæopteryx.
- Sub-class 2.—Odontornithes: Ichthyornis, Hesperornis.
- Sub-class 3.—Ratitæ: Smooth sternum.
- Sub-class 4.—Carinatæ: Keeled sternum.
Class 8.—Mammalia. Animals having the body covered with hair; warm-blooded; young nourished with milk secreted from mammary glands; lower jaw articulating directly with the skull, the quadrate becoming the malleus (ear-bone); heart four-chambered and with the aorta reflected over the left bronchus; red blood-corpuscles non-nucleated; complete diaphragm; brain large, especially the cerebrum and cerebellum; uterine gestation; viviparous.
- Sub-class 1.—Ornithodelphia: Order Monotremes. Urinary and genital canals opening into cloaca. Laying large eggs.
- Sub-class 2.—Didelphia: Order Marsupials. Animals having pouch for protection and growth of prematurely born embryos.
- Sub-class 3.—Monodelphia: Placental Mammals.
- Order 1.—Edentata.
- Order 2.—Rodentia.
- Order 3.—Insectivora.
- Order 4.—Cheiroptera.
- Order 5.—Cetacea.
- Order 6.—Sirenia.
- Order 7.—Proboscidea.
- Order 8.—Hyracoidea.
- Order 9.—Ungulata.
- Order 10.—Carnivora.
- Order 11.—Primates.
Primates are an order of Monodelphia or Placentalia, including lemurs, monkeys, and man. They are nearly all adapted to an arboreal life. The hand (manus) and the foot (pes) nearly always have five digits provided with flat nails. The pectoral and pelvic limbs are prehensile, owing to the fact that the thumb (pollex) and big toe (hallux) are more or less completely opposable to the other digits. The orbital fossa is completely surrounded by a bony rim. The femur does not have a third trochanter. The internal condyle of the humerus does not have a foramen above it. The clavicles are always well developed. The testes descend into a scrotum. On the thoracic region there are nearly always two teats. The placenta may be non-deciduate, or deciduate and metadiscoidal.
The order of Primates is subdivided into the following sub-orders, viz.:
- Sub-order 1.—Lemuroidea.
- Sub-order 2.—Anthropoidea.
Lemuroidea. The Lemurs are small, monkey-like quadrupeds. They are mostly nocturnal, arboreal creatures of comparatively low organization. The body is furry. The orbital and temporal fossæ freely communicate. The lachrymal foramen is situated outside the orbital fossa. The dentition of the Lemurs varies greatly; in some of them it is 2/2 1/1 3/3 3/3 for both jaws. In nearly all of them the median incisors of the upper jaw are separated by a median space. Both feet have flat nails on all the digits, except the second of the hind-foot, which has a claw. The thumb (pollex) and the big toe (hallux) are well developed. The cerebral hemispheres are only slightly convoluted, and do not entirely overlap the cerebellum. The transverse colon is almost always folded on itself. There may be a pair of teats on the abdomen. The uterus is two-horned, and the placenta is diffuse.