BIRD. the puflin. At the base of the upper mandible, a portion of the beak is covered with a mem- brane, called the cere (Lat. ccra. wax, from the waxy appearance which it presents in some fal- cons, etc.), which in many birds is naked, in others is feathered, and frequently is covered with hairs or bristles. The nostrils are situated in the upper mandible, usually in the cere, but in some birds they are comparatively far forward, and in some, as puffins, they are very small and placed so near the edge of the mandible as not to be easily detected. 'I'hey are more or less open, or covered with membrane, or protected by hairs or feathers. Besides their principal use for seizing and dividing or triturating food, the bills of birds are employed in a variety of func- tions, as dressing or preening the feathers, con- structing nests, etc. They are also the principal instruments used by birds in their combats. The Feet. — The feet of birds vary considerably, according to their mode of life. In some the claws are strong and hooked, in others short, straight, and weak; in some the toes are all sepa- rate, in others more or less connected ; in birds especially adapted for swimming they are gen- erally a-ebhcd or united by a membrane; in other swijuming birds, however, a membrane extends only along the sides of each toe, A large group of birds, including woodpeckers, parrots, etc., have two toes before, opposed by two behind, the foot being thus particularly adapted to grasping irregular surfaces and facilitating climbing. These distinctions were seized upon by the early ornithologists as a means of classification, which gave us such obsolete group-names as Scan- sores, Kasores, etc., which only partly coincide with the more scientific groupings now accept- ed. In most birds the tibia is feathered to the heel-joint : in some, however, and particulai'ly in unders, the lower ])art of it is bare : the shank and toes are generally destitute of feath- ers, and are covered with scaly skin, and the arrangement of these scales has been much stud- ied. "The most primitive form of the horny covering of the feet." according to Stejneger, "seems to be its division into uniform hexago- nal scales, and is called reticulate: the next .stage is when some of these scales fuse together, forming what are termed scuta, or scutella ; . . . still further s]iecialization is indicated by the tarsal scuta fusing into a continuous covering, which, iu its extreme development, embraces both the front and the back of the tarsus, as in some of the higher groups of passerine birds; such a tarsus is said to be 'booted.' " Feet, like beaks, have certain accessory or changeable parts; thus in the grouse family there is a seasonal molting ot the sheaths of the claws. The most important appendage, however, is the spur or series of spurs, which arm the 'heels' of .certain gallina- ceous cock birds, and form serviceable weapons among this da.ss, whose beaks are ill adapted to use as weapons, so that they strike with feet and wings in their combats. The extraordinary development of the legs and feet in ratite birds will be fonnd described under MoA, Ostrich, and similar titles. Oihdlaiid. — The skin of birds has no sudorifer- ovis nor sebaceous glands, but on the rump at the base of the tail (on the 'pope's nose') is a bilobed gland containing oily matter, which is present in all birds except the RatiUe, bustards. and a few others. This secretion seems useful 98 BIRD. only for cleaning the plumage, and the bird squeezes a little out upon its beak before preen- ing its feathers. In the oil-bird tlie .secretion is excessive, and that of the hoopoe has a very disa- greeable odor. IxTERN'.i. Structure. Skeleton. — The theory and facts of ancestry related above are enforced by comparative anatomy, which finds in the structure of birds a close resemblance to the internal structure of reptiles. Birds, neverthe- less. ))Ossess distinctive anatomical features fully entitling them to rank as a sejiaratc class. In general form the body is spindle-shaped, tajiering forward from the shoulders to the head, with the feathers sloping backward, and again dimin- ishing toward the tail; this is adajitive to prog- ress through the thin media of air and water inhabited by birds; and the weight is thrown forward, securing proper balance for the nor- mally horizontal position. In order to secure this there is a concentration of muscles and other organs in the region below the point of suspension of the wings. Not only are the fleshy portions of the legs mainly confined to the upper portions of these limbs, but the muscles which elevate the wings are actually placed on the under instead of the upper surface of the body. Though the neck is sometimes much |)rolonged, the body is very compact and rigid. The back- bone consists of vertebra- having (typically) sad- dle-shaped, articular facets, and many processes and ligaments which lock them firmly together; moreover, the vertebne of the liack generally be- come ankylosed or firmly united together by ce- menting bone, the solidity thus acijuired being for the support of the ribs, and these also are proportionately stronger than is usual in mam- mals; each of them is provided in the middle with a flattened bony process, directed obliquely back- ward to the next rib, so that they su])port one another, and they often Reconie ossified with the sternum, giving unusual rigidity and strength to the thoracic framework. The hinder part of the spine is consolidated with the pelvis, and the tail, primitively long, has become shoi-tened into a few small movable vertebra- terminating in a short and generally much elevated Ixme, consisting of ankylosed vertebne, called the pygo- style, or ])lowsharc bone. In contrast to the general stiffness of the ver- tebral cohinm in the trunk, it is remarkable for great fiexibility in the neck, enabling a bird to make ready use of its bill, or to bring its head into such positions as suit the adjustment of the centre of gravity in flying, standing, etc.; there are also certain peculiar ligamentous bands, by which birds can retain the neck in the customary S-curve without muscular exertion. The first (atlas) and second (axis) vertebra- are modified to form an articulation with the head, which is completed by a single globular condyle (as in reptiles), forming a sort of pivot, and enabling the head to be turned around with a freedom and to an extent im])ossible to the mam- malia; and the fact that it is formed almost wholly by the basioccipital bone constitutes a fun- damental distinction between birds and the rep- tiles on one side and the nuunmals im the other. The Sl.tiH. — The skull is formed of bones cor- responding with those of man: but they can be distinguished only when the bird is very young, soon becoming cons(didated together. The brain- case "is more arched and spacious, and is larger. i 1
