1500 



VOICE. 



larynx differs in structure from that of any other 

 order of birds. They have no os transversale 

 dividing the vocal organs, which is conse- 

 quently a single larynx. The segments of 

 the rings in which the lower end of the trachea 

 terminates are consolidated together on each 

 side. The last two of these segments are of 

 a crescent-like or semilunar form, with its 

 axis nearly perpendicular to the axes of the 

 ring of the trachea ; they are concave to 

 each other, and their extremities articulated 

 together, forming an elliptical space which is 

 furnished with a thin vibratile membrane, as 

 seen in jig. 917. At their junction is the 

 joint or axis on which they revolve upon each 

 other, and by which the tension of the mem- 

 brane of the glottis is capable of being varied. 



Fig. 917. 



Inferior Larynx uf the Parrot, 

 a, b, tensors of the glottis ; c, laxator of glottis. 



The glottis is formed on each side by the 

 elastic membranes that fill the space between 

 the semilunar bones]; these membranes leave 

 a narrow chink between them through which 

 the air from the lungs passes, and puts them 

 in a state of vibration whenever the bird 

 draws them sufficiently tense ; for this pur- 

 pose they are provided with three pairs of 

 muscles, of which two , b, are tensors, and 

 one c laxator of the glottis. 



The trachea of birds comprehends that 

 portion of the vocal tube which lies between 

 the superior and inferior larynx j its diameter 

 and length generally depend on the length of 

 the neck of the bird. In the common crane, 

 the trachea after making its exit from the 

 thorax, penetrates the sterno-tracheal space, 

 and then making four turns upon itself in the 

 same plane, it leaves the breast bone to 

 follow its course into the neck : by this ar- 

 rangement the vocal tube is greatly lengthened 

 for the purposes of voice, and the surface of 

 the sternum increased for the attachment of 

 the great pectoral muscles without adding 

 materially to the weight of the bird. The 

 voice of the crane is very sonorous, and may 

 be heard at a great distance. 



In Bewick's swan (fg. 918), the manner in 

 which a considerable additional length is 

 given to the trachea by its convolutions, will 

 be evident upon an inspection of the figure. 



The spoonbill presents another remark- 

 able instance of convoluted trachea, doubling 

 twice upon itself. Other examples of con- 



voluted trachea are found in the Gal- 

 linaceae ; as in the Rhynchcea Australis, and 

 Phasianus Purraqua. In the singing birds 

 the trachea is a cylindrical tube ; the rings 

 which are at first cartilaginous become ossi- 

 fied with age. The tracneal rings, which are 

 entire in the adult state, being connected by 

 elastic membranes, are at a sufficient distance 

 from each other to allow of all the movements 

 of the neck. 



Fig. 918. 



Inferior Larynx and convoluted Trachea in Bewick's 

 Swan, from Yarrell. 



The diameter of the trachea in singing 

 birds is nearly uniform and proportional to 

 its length ; but among the Palmipedes, the 

 Mergansers, and some species of Anas, as the 

 A.fnsca and A. rufina, there are tracheal en- 

 largements with additional muscles, to control 

 their dimensions. The number of rings in the 

 trachea of some birds is very great, sur- 

 passing that of any other class of animals. 

 In the Phcerticopterus, according to Dr. Grant, 

 there are at least 350 rings. 



PHYSIOLOGY OF THE VOICE OF BIRDS. 

 The vocal apparatus of birds consists of the 

 lungs, larynx, and trachea, representing a wind 

 chest, reed, and pipe. The inferior larynx 

 has been proved by Cuvier to be the organ in 

 which the sounds are generated. To ascertain 

 this fact, he divided the trachea of a black- 

 bird about the middle of its length, thus pre- 

 venting the passage of the air through the 

 superior orifice ; the bird notwithstanding con- 

 tinued to sing, though the tones were more 

 feeble than before. In a second experiment 

 on the pie, performed in the same manner, the 

 bird cried with as great intensity of tone, and 

 with the same acuteness as before the opera- 

 tion, for the space of about ten minutes 

 when the blood from the wound being drawn 

 into the larynx suffocated the animal. These 

 experiments, however, were sufficient to prove 

 that the sound did not arise from the superior 

 larynx ; and when we view the structure of 

 that organ, and, find it destitute of vocal 

 ligaments, or any salient membranous laminae, 

 and bounded by cartilaginous or osseous 

 matter, and compare it with the complex 

 organization of the inferior larynx, we might 





