AYES. 



315 



mechanical assistance which they afford to the 

 muscles of the wings. This was first suggested 

 to us by observing that an inflation of the air- 

 cells in a Gigantic Crane (Ciconia Argala) 

 was followed by an extension of the wings, as 

 the air found its way along the brachial and 

 anti-brachial cells.* In large birds, therefore, 

 which, like the Argala, hover with a sailing 

 motion for a long-continued period in the 

 upper regions of the air, the muscular exertion 

 of keeping the wings outstretched will be les- 

 sened by the tendency of the distended air-cells 

 to maintain that condition. It is not meant to 

 advance this as any other than a secondary 

 and probably partial use of the air-cells. In 

 the same light may be regarded the use as- 

 signed to them by Hunter, of contributing to 

 sustain the song of Birds, and to impart to it 

 tone and strength. It is no argument against this 

 function that the air-cells exist in birds which 

 are not provided with the mechanism necessary 

 to produce tuneful notes ; since it was not pre- 

 tended by Hunter that this was the exclusive 

 and only office of the air-cells. The latest 

 writer on this subject has indeed proposed this 

 suggestion of Mr. Hunter as a novel idea.f 



Air-passages. The air-passages in birds 

 commence by a simple superior larynx, from 

 which a long trachea extends to the anterior 

 aperture of the thorax, where it divides into 

 the two bronchi, one to each lung. At the 

 place of its division there exists, in most birds, 

 a complicated mechanism of bones and carti- 

 lages moved by appropriate muscles, and 

 constituting the true organ of voice : this part 

 is. termed the inferior larynx. 



The tendency to ossification, which is ex- 

 emplified in the bony condition of the costal 

 cartilages and tendons of the muscles, is again 

 manifested in the framework of the larynx and 

 the rings of the trachea, which, instead of 

 being cartilaginous, as in Reptiles and Mam- 

 mals, are in most birds of a bony texture. 



The superior larynx (Jig. 151, 174, 175,) 

 is situated behind the root of the tongue, and 

 rests upon the uro-hyal element of the os hy- 

 oides, to which it is attached by dense cellular 

 texture. 



It is composed of several bony and cartila- 

 ginous pieces, varying in number from four to 

 ten. The largest oi these pieces constitutes 

 the anterior part of the larynx. It is of 

 an oval or triangular form, according as. its 

 superior termination is more or less pointed : 

 it is regarded by Cuvier as analogous to 

 the anterior part of the cricoid cartilage, 

 (Lecons d'Anat. Comp. iv. p. 489,) but by 

 Carus it is considered as representing the 

 thyroid cartilage (f y fig. 151). The cricoid 

 cartilage in birds consists of the three osseous 

 pieces, which are situated at the posterior 



* On relating this fact to Mr. Clift, he suggested 

 another use of the air-cells which is more generally 

 applicable, namely, that of assisting the actions of 

 the muscles by compressing and bracing them, in a 

 manner analogous to the action of the fasciae of the 

 extremities in Man. 



t Jacquemin, Memoirc sur la pneumaticitc des 

 oiseaux, 1835. 



Fig. 174. 



and inferior part of the upper larynx; the 

 middle one (g,Jig. 151) is of an oblong form, 

 and varies in size, being larger than the lateral 

 ones in the Anatida, but smaller in the In- 

 scssores. The lateral pieces are connected at 

 one extremity with the thyroid piece, and at 

 the other to the middle oblong piece above 

 described, which completes the circle of the 

 laryngeal frame-work posteriorly. Carus re- 

 gards the first two incomplete tracheal rings 

 (gg) as the anterior part of the cricoid. The 

 arytenoid bones (h) rest upon the middle ob- 

 long portion of the cricoid, and extend for- 

 wards, being connected at their outer edge by 

 means of elastic cellular substance to the thy- 

 roid bone, and attached by their anterior ex- 

 tremities to the uro-hyal bone by means oi" 

 two small ligaments :* they form, by their inner 

 margins, the rima glottidis or laryngeal fissure. 

 This fissure (i,fig. 152) being thus bounded 

 by inflexible rigid substances is only susceptible 

 of having its lateral diameter varied according 

 to the degrees of separation or approximation to 

 which the arytenoid bones are subject. These 

 different states are produced by (appropriate 

 muscles, one pair of which may be regarded 

 as analogous to the Thyreo-arytcnoidei, and the 

 other may be termed Constrictores glottidis. 

 The former of these muscles (k k,Jig. 174,) 

 arise from the sides and posterior surface of 

 the thyroid bone, and are 

 inserted into the whole 

 length of the inner edge 

 of the arytenoid cartilages, 

 which they draw out- 

 wards, and consequently 

 open the laryngeal fissure, 

 The constrictores glottidis 

 in the Gigantic Crane arise 

 from the middle of the in- 

 ternal or posterior surface 

 of the thyroid bone, and are 

 inserted into the extremi- 

 ties of the arytenoid pieces. 

 According to Mr. Yarrell, 

 from whose Memoir the subjoined figures are 

 taken, the constrictors of the glottis (l,fig.175) 

 " pass from the upper portion of the cricoid 

 (thyroid) cartilage along the cru'ra of the ary- 

 tenoid cartilages, upon each outer edge of 

 which they are inserted ."-f 

 In either case these muscles 

 are enabled to close the la- 

 ryngeal opening with con- 

 siderable force, and with 

 such accuracy as to super- 

 sede the necessity of an 

 epiglottis. From the sim- 

 plicity of the structure just 

 described, from the situation 

 of the superior larynx with 

 relation to the rictus or gape 

 of the bill, and from the 

 absence of lips by which 

 this might be partially or 



* Linn. Trans, vol. xvi. p. 06, pi. 17, figs. 

 3 and 4. 



t This description is taken from the Gigantic 

 Crane. Ciconia Argala. 



Fig. 175. 



