210 GENERAL ORNITHOLOGY. 



the floor of the mouth, at the root of the tongue, between the forks of the hyoid bone, resting 

 upon the uro-hyal. Besides its attachments of mucous and other membrane, it is connected 

 with the hyoid bone by a pair of thyro-liyoid muscles (8, l»i), and usually with the rest of the 

 trachea by prolongations of the steruo- and cleido-ti'acheales. It is usually a small, simple, 

 conical " mouth-piece " of the pipe (4, a), without the dilatation which renders the corresponding 

 structure — the " Adam's apple," — so conspicuous in the human throat. Below, it communi- 

 cates directly with the pipe : above, it opens into the mouth by the glottidean fissure, or rima 

 glottidis (3, c), a median lengthwise chink, which opeus and shuts as its sides diverge or close 

 toiiether, and which is further defended in front by a folding of the mucous membrane of the 

 mouth, constituting a rudiment of that curious trap-door arrangement which, when fully 

 developed, is called the epiglottis (3, d, e). Exclusive of two broken upper rings of the tra- 

 chea (6, g), the cartilages (or oftener bones, — for they generally ossify) of the larynx are five. 

 One is a large single median and inferior piece, the thyroid, or shield-jiiece (*, ^, ", a), 

 forming the most substantial part of the structure. It is somewhat triangular or oblong, run- 

 ning to an obtuse end in front ; and with sides and posterior angles which curl upward behind. 

 To its lateral posterior corner is attached on each side the small "horns" or cornicula laryngis 

 (5. 6^ 7^ i>). There is a small median upper posterior piece, supposed to represent all there is 

 of the cricoid (5, T, c), which in man makes a ring around the larynx below the thyroid. To 

 the cricoid, as to a base, are attached a pair of straight slender arytenoids (6, 7, d), projecting 

 forward along the upper surface of the larynx : these form the rima glottidis, — the fissure of the 

 glottis being between them. The arytenoids are attached in front by slender ligaments to the 

 end of the thyroid (5, the little slips between d and e), and they are supplemented by carti- 

 laginous edges {^, f,f) ; but there are no true vocal chords. Besides the extrinsic thyro-hyoid 

 muscles, which pass from the larynx to the tongue-bone, the laryngeal parts are operated by 

 intrinsic muscles, the sum of the motion given by which is the opeuiug and shutting of the 

 glottis by drawing apart or pulling together the arytenoids. Four pairs of such muscles are 

 described for some birds. As named and figured by Macgillivray for the rook, there are : the 

 thy ro- arytenoids, which are the openers of the glottis (9, 2,2) ; the oblique arytenoids (lo, 3,3) ; 

 the thyro-cricoids ('i, 4,4); and t\ie posterior thyro-cricoids Q-^ and ^2^ 5,5). 



The Syrinx (Gr. a-vpiy^, surigx, a pipe) or Lower Larynx is the voice-organ of birds; in 

 most respects a more complicated structure than the larynx proper, and one so differently 

 constructed in difi"erent birds that it afibrds characters of great significance in classification. 

 The highest group of Passeres, for example, is signalized by the elaboration of this musical 

 organ, the marvellously adroit fingering of the keys of which by the little muscular performers 

 sends through the tracheal sounding-pipe the tuneful messages of bird's highest estate. A few 

 degraded or disgraced birds, as the ostrich and the American vultures, have no bucolic organ at 

 aU, the trachea forking as simply as possible. Others, as the common fowl, have a fair syrinx, 

 but no muscles whatever to modulate their pastoral lays. Others have one, two, or three pairs 

 of intrinsic nmscles; to which may or may not be added a stemo-tracheal with syringeal attach- 

 ment. It is not so much the bulk or mere fleshiness of the syrinx that indicates musical abil- 

 ity ; but the distinctness of the several muscles, and the mode of their insertion, which result in 

 endless combinations of rotating and rocking movements of the parts, whereby an infinite modu- 

 lation of the musical tones becomes possible. In Oscines, there are normally five or six pairs 

 of muscles, without counting the extrinsic sterno-tracheales ; and the gist of the arrangement, 

 in these melodious Passeres, is the attachment of the muscles to the ends of the upper bronchial 

 half- rings, as far as the third one. As Professor Owen remarks with appreciative feeling, "the 

 manifold ways in which the several parts of the complex vocal organ in Cantores may be 

 afi"ected, each of the principal bony half-rings, as one or the other end may be pulled, being 

 made to perform a slight rotatory motion, are incalculable ; but their efiects are delightfully 



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