Sauropsida
a primary group or province of vertebrata, comprising reptiles and birds. An epidermic skeleton, in the form of scales or feathers, is almost always present. The centra of the vertebræ are ossified, but have no terminal epiphyses; the the skull has a completely ossified occipital segment; mandible always present, and each ramus consists of an articular ossification, connected with the skull by quadrate bone. The apparent ankle joint is situated between the proximal and distal divisions of the tarsus, not between the tibia and the astragalus, as in the mammalia. The heart is tri- or quadri-locular, and some of the blood corpuscles are red, oval, and nucleated. Respiration is never effected by means of branchiæ, but after birth is performed by lungs. The cerebral hemispheres are never united by a corpus callosum. The reproductive organs open into the cloaca; the oviduct is a Fallopian tube with a uterine dilatation in the lower part. All are oviparous or ovoviviparous; there are no mammary glands; the embryo has an amnion and a large respiratory allantois, and is nourished at the expense of the massive vitellus.