“ Most of the bones are solid or have cavities filled with marrow, the air cells which aid in imparting lightness to the bones of birds being, as a rule, absent. The bones of the cranium and of the face are immovably fixed to each other. The cranium is larger than in other vertebrates, the lower jaw consists of only two pieces. ”

“ The vertebral column may be divided into five regions, the cervical, the dorsal, the lumbar, the sacral, and the caudal vertebræ. The heart has two auricles and two ventricles. The respiration is by lungs. ”