(a) scales, which cover the toes and tarso-metatarsus;
(b) claws, which are attached to the distal phalanges of the toes and of the pollex;
(c) the wide beak, which sheaths both upper and lower jaws, and whose edges are raised into lamellae, which act as strainers.
Feathers.
A well developed feather, such as one of the large quill feathers of the wing or tail, consists of the following parts: A main stem, the scapus, which forms the axis running along the whole length of the feather, and is divided into (1) a proximal hollow cylindrical portion, the calamus or quill, and (2) a distal solid portion, the rachis or shaft, which is square in section, flexible and grooved along its ventral surface, and bears a number of lateral processes, the barbs. The calamus which is partly imbedded in a pit in the dermis, bears two holes: one, the inferior umbilicus, is at its proximal end, and into it enters a vascular outgrowth from the dermis; the other, the superior umbilicus, lies on the ventral surface at the junction of the calamus and scapus.
The barbs are a series of narrow elastic plates, attached by their bases to the rachis, and with their edges looking upwards and downwards. The barbs are connected together by a number of smaller processes, the barbules, which interlock with one another by means of hooklets, and bear the same relation to the barbs that the barbs do to the rachis. The barbs and barbules, together with the rachis, constitute the vexillum or vane of the feather. Any feather having the above type of structure is called a penna or a contour feather, from the fact that it helps to produce the contour of the body.
Varieties of feathers.
1. Pennae. There are two kinds of pennae or contour feathers.
(a) The quills. These form the large feathers of the wing and tail. They are divided into two groups, the remiges, or wing quills, and the rectrices, or tail quills.
The remiges[101] include three sets of feathers, the primaries or metacarpo-digitals, which are attached to the bones of the manus, the secondaries or cubitals, which are attached to the ulna, and the humerals, which are attached to the humerus.