BIRDS. 369 



with each other at their extremity, and forming an elongated oval 

 ring. There is a fenestra of the cochlea and a fenestra of the vesti- 

 bule; the last, or fenestra ovalis, is the superior and larger; close 

 below it lies the fenestra of the cochlea, which has also an oval 

 form, and so the name fenestra rotunda is scarcely applicable to it. 

 The ossiculum auditus is stiliform, and terminates in an oval or tri- 

 angular plate, by which it rests upon the fenestra of the vestibule. 

 The apertures of the Eustachian tubes lie close together in the 

 palate behind the internal openings of the nasal cavities. The 

 membrane of the tympanum has its external surface convex. The 

 external meatus is short ; its opening is surrounded by a circlet of 

 feathers sometimes of a peculiar form, which in certain birds are 

 elongated and extend beyond the other feathers of the head. In 

 the owls there is a cavity in front of the external meatus furnished 

 with various folds of skin, which in some degree corresponds to an 

 external ear 1 . 



The muscles in this class are arranged in a way corresponding 

 to the peculiar mode of life in birds. The cutaneous muscles are 

 strongly developed, which are divided into numerous distinct 

 parcels, and do not form such a continuous layer (panniculus car- 

 nosus] as is present in mammals. 



The quills or stiffer feathers on the surface of the body have 

 proper small muscles, produced from the cutaneous muscular layer, 

 for each feather four or sometimes five in number, so that the whole 

 number may be reckoned at more than 12,000 2 . The other muscles 



1 See on the auditory organ of birds SCABPA De Auditu et Olfactu, pp. 32 36, 

 TREVIRANUS Ueber den innern Bau der Schneclce des Okrs der Vogel, Zeitschr. f. 

 Physiol. I. s. 188196, Tab. IX. ; WiNDisCHMANN De penitiori in Amphib. struc- 

 tura, pp. 78 36 (with which again compare TKEVIBANUS Die Erscheinungen u. 

 Gesetze des organ. Lebens, 1832, 11. s. 119, 120); BBESCHET Rech. anat. et physiol. 

 sur rOrgane de Vouie dans les Oiseaux, Ann. des Sc. not., 2e Se*rie, Tom. V. Zoologie, 

 PP- 552, PL I. n. 



2 NITZSCH, quoted by CARDS Vergl. Zoot. I. s. 294. Some cutaneous muscles 

 compress the air-sacs situated under the skin; they have been described by OWEN 

 in Sula alba, Proceedings of the ZooL Soc. Part I. 1830, 1831, p. 91. OWEN has 

 described also, at length, the cutaneous muscles in Apteryx, where they are more than 

 commonly developed ; this is connected with the peculiar thickness of the skin and 

 probably also with the habit of this bird to roll itself on the ground, when it has 

 its use in shaking the loose earth from the feathers. Proceedings of the Zool. Soc. X. 

 1842, pp. 2224. 



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