BIRDS, in Latin Ares, in Greek 'Opralts (whence a class of Vertebended, Oviparous, Feathered Bipeds, generally formed for flight. We say generally, because, though their mechanism is ih its most perfect development designed for enabling them to support their bodies in the air and to make progress in that medium, it is also calculated for motion on the ground and for perching on trees. Some families indeed are framed entirely for moving on the ground, and others for that motion and for making their way both on the surface of the water and even for a short period below it, without the power in either case of raising themselves into the air.
• Skeleton.
Skull (Cranium). The first peculiarity which strikes an observer, I when comparing the skulls of birds with those of mammifers, is the absence of sutures in the former, the proper cranial bones being consolidated into one piece. The skull of birds le articulated to that part of the vertebral column called the neck by a single condyle or Lac5phde describes the body and tail of P. lepidopodus as being nearly cylindrical, very slender, and a little like those serpents called by the French Greets, of which our common Blind-Worm or Slow- Worm (Anyuis fragilis, Linnaeus) is an example ; and which, though without limbs, have some of the rudiments of such members in the skeleton. The upper part of the head of P. lepidopodus is covered by seven large scale-plates disposed around an eighth, which is a little larger than the others. Each eye is surrounded by small scaly globules. The gape is sufficiently large, and the tooth are equal and small. The fiat long tongue is without a notch. The auditory orifice is near the commiesure of the lips. The scales which cover the upper part of the body are lozenge-like, striated, and small, especially those which cover the most elevated part of the back ; but the scales of the under part of the belly and the tail are hexagonal and smooth, and those of the two middle longitudinal ranks are larger than those of the lateral ranks. At each extremity of the curve formed by these tubercles ie to be seen a foot, in which no finger is to be distin guished externally, and which is surrounded by very small scales on its lower part, and by scales a degree lens small on its upper surface. The colour is greenish, varied with some very small black
blotches.
"Thin reptile," says Lacdpede, "like the other species of Biped, ranks between the oviparous quadrupeds and the serpents ; it is related to the latter by its general form, as well as by the figure, proportion, and distribution of tho scales, while it approaches the joint, which is situated at the front margin of the great occipital opening (foramen magnum), through which the brain, becoming elongated as it were into the spinal cord, descends into the vertebral column. It is this beautiful adaptation of structure to the wants of the animal that gives such a freedom of motion to the head, especially in a horizontal direction. Take for example the Wryneek (Tuns torquila), which, as those who have eurpnsed the bird on the nest will readily admit, can writhe her head round so as to look the intruder in the face, hissing all the while like a snake ; by this 'terrible show' many a birds-neating novice is frightened away. Perfect repose in a bird seems hardly to be enjoyed without turning back the head and nestling the beak between the wings ; this attitude the articulation above mentioned enables the bird to command with the least possible effort.
The orbits are very large in proportion to the Ault, to which last the lower jaw Is joined by a somewhat square bone (os quadratum) not far from the ear. A small bone rests on the square bone at one end, while the other end comes against the palate. When therefore the square bone is brought forward by depressing the lower jaw, and also by muscles adapted to the purpose, the small bone presses up against the palate, and this raises the upper jaw, which contrary to the rule in the structure of mansinifers is in birds, with but few exceptions, thus gifted with motion.