The Bird's Bill or Beak

The Rhamphotheca or Horny Sheath

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Tbe Bird's Beak or Bill and the Rhamphotheca or Horny Sheath

Bird Nostrils

Sifting Bills, Spatula and Spoonbills

Birds with Strong Beaks including Hornbill, Crossbill and Wry Bill

Egg Tooth and Gender Dimorphic Bills

In Latin a bird's bill or beak is known as the Rostrum. This consists of an upper, chiefly premaxillary and maxillary, and of a lower, or mandibular, half. The horny covering is to a certain extent moulded after the shape of the supporting bones. The soft cutaneous portion of the skin is frequently restricted to a thin layer between the periosteum and the Malpighian layer of the epiderm; in it run numerous blood- vessels and nerves, the latter occasionally penetrating the horny layer, and ending in tactile or sensory corpuscles.

On the other hand, in very stout beaks, the cutaneous layer forms conical elongations which project into the thick horny parts, especially into the ends of the upper and lower bill. In the broad edge of the mandible of Parrots such projections are particularly numerous and long; when they calcify, as cutaneous structures are liable to do, they bear in horizontal sections a superficial resemblance to the germs of teeth, and have been mistaken as such by various anatomists (see TEETH).

The  Rhamphotheca

The horny sheath, or rhamphotheca, is produced by the outer layers of the Malpighian cells, and resembles in structure other horny parts, as claws, nails, and spurs. The horny sheath of the bill sometimes consists of a number of pieces more or less separate. In the Ostriches and Tinamous there is a lateral pair and an unpaired piece for each jaw; in the Tubinares on the upper jaw at least one pair of lateral or maxillary pieces, an unpaired piece which covers the culmen and is continued into the prolonged nasal tubes, and an apical hook, strongly curved and pointed: each half of the under jaw is covered by one ventral, one dorsal, and one terminal piece, the latter partly fusing with that of the other side into a strong scoop.

Indications of such a compound rhamphotheca are, however, found in other birds, especially in the Steganopodes, in some Herons, like Nycticorax and Scopus, and in Penguins; the culminar or dorsal unpaired piece being more or less separated from the lateral pieces. In the majority of birds the horny covering forms one coherent sheath.  Sometimes, as in the Anseres, the greater portion of the outer sheath of the bill is soft, and only the tip of the bill is transformed into a thick horny "neb," which contains numerous tactile organs.
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