COMPARATIVE ANATOMY AND FHYSIOI.ocY OF THE ORGANS OF VOICE. — Having given an outline of the structure and functions of the vocal organs in man, and stated our views of the principles on which the produc tion of voice depends, we shall now proceed to the investigation of the physiology of voice in the lower animals.
1M?annoa/za.—In the various orders of mam malia the organs of voice present different grades of development and complexity of structure, producing in each case some pecu liarity of timbre, or quality of tone, by which we are enabled to distinguish them front one another. Some species are mute, such as the giraffe, armadillo, and others, whilst some possess voices of greater or less intensity.
The organs of voice in the lower mammalia, as well as in man, are composed of lungs, which, considered in an acoustic point of view, act merely as bellows, the trachea or pipe, and the larynx* or reed. The nervous and mus cular systems are similar to those of man, and do not require to be treated in detail. The acoustic principles of the first section will generally be applicable to the lower orders of Mammalia, so that when the structure is given the functions will be understood.
In the account of the anatomy of the vocal organs given by Cuvier, Vicq d'Azyr, Brandt, Wolff, HenI6, and others, no estimate is made of the relative dimensions of the larynx in the various classes of animals ; therefore, in order that the reader may form an idea of their magnitude in Mammalia, compared with that of man, t it will only be necessary, in those which have a similarity of figure, to give the linear value of one of their dimensions, namely, that of the mean height of the superior margin of the thyroid, above the plane of the base of the cricoid, since their respective magnitudes will be as the cubes of those heights.t Also the lengths of the inferior thyro-arytenoid liga ments, when devoid of tension, are given. The letters H and L will be used to represent the heights and lengths respectively.
QUADRIMIANA.—The vocal organs of the Quadrumana have already engaged the atten tion of several distinguished anatomists, such as Vicq d'Azyr, Camper, Hunter, Cuvier, Brandt, and others ; and a condensed view of this part of the subject will be now given.
Chimpanzee.— Os hyoides : base concave, where a sac b (fig. 894) is lodged. Larynx, H. 0.8 in. Thyroid : margins, superior and in ferior, nearly parallel. Corium short; supe rior inclined upwards and backwards, inferior inclined downwards and forwards. Cricoid elliptical : margins, superior triangu!ar, notch in front; inferior parallel to the first ring of the trachea, except in front, where it is de 1 ressed. Arytenoids small. Cuneiform curved, and in contact with the anterior margin of the arytenoids. Cart. Santorini — inferior thyro-arytenoid ligaments prominent. L. 0.5 in. to 0.6 in., superior thyro-arytenoid ligament not prominent. Ventricles of Illor gagni oval, deep, leading to sac (a, a), lying between the epiglottis and arytenoid carti lage ; right sac anterior to the left, convo luted, terminating in the concavity of os by oides (c). Epiglottis : apex obtuse, trachea 16 rings. Voice more acute than in women ; quality inferior: cause, sacculated larynx, &c.# Orang-outang. — Larynx : volume equal to chimpanzee. Thyroid : wings united at an obtuse angle : margins, superior notched in mesial line. Cornua short. Cricoid ellipti cal : margins, superior and inferior, depressed in front ; the latter connected with the first ring of the trachea. Crico-thyroid chink large. Arytenoids small. Cuneiform large and curved. Cart. Santorini : vocal ligaments, inferior prominent ; L. less than in woman. Ventricles oval, furnished with a canal pene trating the thyro-hyoid membrane. Sacs large, lie on each side the larynx. Ventricles valvular, rendering the inflation of the sacs under the control of the animal. Epiglottis broad, apex obtuse.* Gibbons.—Os hyoides : base not excavated. Larynx, volume nearly equal that in orang ; ventricles deep, communicating with a sac in Hylobates agilis, which lies in front on the thyro-hyoid membrane. Voice acute. Cry, bow wow.