. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 308 AVES. acini of the cells proceed. In the Albatross and Penguin we have traced two or three distinct ducts leading from this gland to the nose. Organ of Hearing.—The structure of the organs of hearing in Birds resembles most closely that in the higher Reptiles, especially the Crocodile. There is no concha, or projecting Fig. Organ of hearing, Owl. auricle in this class, for collecting and con- densing the rays of sound; but to compen- sate for this deficiency, the labyrinth, and especially the semicircular canal
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 308 AVES. acini of the cells proceed. In the Albatross and Penguin we have traced two or three distinct ducts leading from this gland to the nose. Organ of Hearing.—The structure of the organs of hearing in Birds resembles most closely that in the higher Reptiles, especially the Crocodile. There is no concha, or projecting Fig. Organ of hearing, Owl. auricle in this class, for collecting and con- densing the rays of sound; but to compen- sate for this deficiency, the labyrinth, and especially the semicircular canals, are of large size in proportion to the cranium. In those Birds, however, which enjoy the locomotive or visual faculties in a less perfect degree than in the rest of the class, there is found a peculiar arrangement of the feathers around the external auditorius, which serves in some degree the office of an external ear. The Ostrich and Bustard (d,fig. 155) are so provided, and these birds can raise the auditory circle of plumes to catch distinctly any distant sound that may alarm them. The Owls, again, are furnished with a large crescentic mem- branous flap, or valve; and the membrana tympani is situated at the bottom of a cavity («, jig. 141), the lining membrane of which is disposed in folds analogous to those of the human auricle. The opercular flap is largely developed in our common Barn-owl (Strix flammea). This species is also remarkable in having the membrana tympani attached ex- clusively to the bony meatus (b,fig. 141), and not to the tympanic bone or os quadratum. The bony framework of the membrana tym- pani is sunk below the surface of the head, and rarely projects so far from the tympanum as to deserve the name of a meatus or canal: it is deficient anteriorly, where it is bounded by the tympanic bone, to which, with the ex- ception above mentioned, the membrana tym- pani is attached for a greater or less extent of its anterior circumference. The drum
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