. Handbook of field and general ornithology; a manual of the structure and classification of birds . he motions of the ball result from consentaneous or dissen-taneous action along these six lines of traction ; the muscles actingas ropes to pull the Ixxll about, and to steady it in any directionof its axis. The peculiarity of mechanism in a bird is, that thesuperior oblique goes straight to its insertion, instead of passing SEC. IV ANA TOMY OF BIRDS 269 through a pulley which changes its line of traction in special nerves presiding over these muscles (3, 4, 6) have beenj)ointed out
. Handbook of field and general ornithology; a manual of the structure and classification of birds . he motions of the ball result from consentaneous or dissen-taneous action along these six lines of traction ; the muscles actingas ropes to pull the Ixxll about, and to steady it in any directionof its axis. The peculiarity of mechanism in a bird is, that thesuperior oblique goes straight to its insertion, instead of passing SEC. IV ANA TOMY OF BIRDS 269 through a pulley which changes its line of traction in special nerves presiding over these muscles (3, 4, 6) have beenj)ointed out already (p. 261). In the figure, the cut orbital ends ofthem all are reflected away from the ball to disclose the underlyingmuscles of the winker: the reader must mentally bring the sixloose ends together and fasten them to the bony orbit at pointsnear about opposite i, as above said of their origins. The above are the principal circumstances and accessories of theoptic apparatus ; we may now examine the eye itself, of which gives an enlarged view, in longitudinal vertical section,—the. Fig. 82.—Vertical antero-posterior section of eyeball: a, optic nerve ; ft, sclerotic, its outercoat; c, sclerotic, its middle and inner coats ; d, choroid ; c, hyaloid ; /, marsupiuin ; (7, cornea ;\ h, bony plates between sclerotic layers; i, i, corrugations of choroid, forming ciliary pro-cesses ; A, fc, canal of Petit; ?, ^ iris ; 7)i, anterior chamber of eye ; 71, capsule of the lens ; 0,lens ; p, posterior chamber of eye. Neither the retina, nor the peculiar sheatliing of the opticnerve, is shown. The nerve, marsupium, and ciliary processes, not falling in this section, canonly be arbitrarily shown. nerve, marsupium, and ciliary processes not indeed lying as shownin this section, but so introduced as to display them birds eyeball is not nearly so spherical or globular as a mam-mals. The globe of the human eye is about a five-sixths segmentof a large sphere (scler
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Keywords: ., bookauthorcouesell, bookcentury1800, bookdecade1890, bookyear1890
