SEC. IV ANATOMY OF BIRDS 305 



bird ; nat. size, after Macgillivray. 1, a, tongue ; &, basibranchial, commonly called urohyal ; 



c, c, horns of hyoid bone ; d, d, geniohyoid muscles ; c, e, stylohyoid muscles ; /, /, clidohyoid 

 muscles : gr, A, i, oesophagus ; j, proventriculus, or secretory stomach ; fc, gizzard, or gigerium, 

 the muscular stomach ; Z, m, %, % intestine, duodenum to rectum ; 0, 3), trachea, or windpipe ; 

 g, inferior larynx, or syrinx ; r, r, right and left bronchus ; ss^_ ss^ contractor muscles of trachea ; 

 *, <, lungs, with u, «, apertures communicating with thoracic air-cells ; v, v, v, thi-ee pairs of 

 muscular slips answering to a rudimentary diaphragm ; 1,2,3,4,5,6,7, as many ribs. — 2. Hyoid 

 bone ; a, glossohyal, tii)ped with cartilage, its posterior horns being ceratohyals proper ; &, 

 basihyal ; c, basibranchial proper, commonly called urohyal ; d, d, ceratobranchials proper, 

 commonly called apohyals ; e, e, epibranchials proper, commonly called ceratohyals, tipped 

 with cartilage, /, /. — 3. Glottis, or opening of trachea in the mouth ; a, base of tongue ; &, b, 

 horns of hyoid bone ; c, rima glottidis, cleft or chink of the glottis ; d, a triangular vacuity ; e, 

 an elastic ligament ; d and e represent an epiglottis ; /, /, a papillose surface. — 4. Larynx viewed 

 from before (below) ; a, thyroid bone or canilage. — 5. Larynx viewed from behind (above) ; a, 

 thyroid bone ; 6, &, its appendages ; c, cricoid ; d, d, arytenoids ; e, e, anterior border of thy- 

 roid, to which d, d are connected by two arytenoid ligaments. — 6. Larynx viewed from right 

 side ; a, thyroid ; b, appendage ; c, cricoid ; d, arytenoid ; /, /, cartilage attached to arytenoid ; 

 g, a tracheal ring. — 7. Larynx viewed from behind ; a, thyroid ; &, 6, ite appendages ; c, cricoid ; 



d, arytenoids.— S, 9, 10, 11, 12. Muscles of the larynx ; 1, 1 (Fig. 8), thyrohjroids ; 2, 2 (Fig. 9), 

 thyroarytenoids, or openers of the glottis ; 3, 3 (Fig. 10), oblique arytenoids ; 4, 4 (Fig. 11), 

 thyrocricoids ; 5, 5, (Figs. 11 and 12), posterior thyi-ocricoids. — 13. Bifurcation of trachea ; aba, 

 last entire tracheal ring. — 14. Last entire tracheal ring, viewed fi-om below, crossed by the 

 pessnlus. — 15. Bif ui-cation of trachea, and. bronchi, viewed from below ; a, pessulus, the bolt-bar, 

 or "bone of divarication" ; &, 6, next succeeding tracheal half-rings. — 16. a, 6, c, d, inferior 

 laryngeal or syringeal muscles, not well made out in this figure ; see text. But the typical 

 oscine arrangement (acromyodian) is perceived, inasmuch as anterior (a) and posterior (d) in- 

 trinsic muscular masses go to ends of the first tracheal half-ring, at b and c ; the extrinsic slip e 

 passing to sternum ; compare Fig. 1 at 2.-17. Trachea, etc., of the nightingale, nat. size. 

 (Compare Figs. 3, 67, 72, 73, 74.) 



of the orifice, is called tte semilunar membrane ; being the edge of a 

 partition common to both bronchi, it forms, in fact, the inner lip of 

 each bronchial orifice ; that is to say, the inner rima glottidis syringis, 

 or lip of the syringeal mouthpiece. This membrane vibrates with 

 the column of air, and is, in fact, one of the " vocal chords." Now 

 the bronchial rings which succeed are not annular, circumscribing 

 the bronchial tube, but are half-rings p, I, h), or arcs of circles to 

 be completed by membrane, which forms more or less (scarcely or 

 not half) of the circumference of the tube ; this membranous part, 

 termed the internal tympaniform membrane Q^, c to c), being on the 

 side of the bronchus which faces its fellow, while the hard bronchial 

 half-rings complete the rest of the cylinder. The membrane is 

 attached to the pessulus above. This accounts for the whole 

 bronchial tube and its vocal septum from its fellow. Now the 

 concavity of the upper two or three bronchial half-rings, on the 

 outer wall of the tube, but in its interior, is the place where is 

 develop'ed a certain fold of the mucous membrane, projecting into 

 the tube opposite the septum, and forming the outer lip of the 

 syringeal glottis; for this membranous fold, like the semilunar 

 membrane, is set quivering in vocalisation. The upper tracheal 

 rings which enter into this arrangement are enlarged and otherwise 

 modified. Thus are formed two " vocal chords," upon the vibrations 

 of which the harmonious or discordant notes of the bird depend. 

 The chords are struck by the hand of air indeed, but endless riusical 

 variations result from the play of the muscles in increasing or 

 diminishing and variously combining the tension of the several 

 parts of the instrument. In giving four pairs of intrinsic syringeal 



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