ORGAN OF THE VOICE.
Aristotle has correctly observed, that those animals only which possess lungs, consequently the three first classes of the animal kingdom, possess a true voice. Several genera and species even of these are either entirely dumb, as the anteater, the manis, the cetacea, the genus testudo, several lizards, and serpents; or they lose their voice in certain parts of the earth, as the dog in some countries of America, and quails and frogs in several parts of Siberia.
Most mammalia have the following cir cumstances in common : their rims glot tidis is provided with an epiglottis, which in most instances has a peculiar muscle, arising from the os hyoides, and not found in the human subject : the mar gins of this rims are formed by the double ligamenta glottidis (ligamenta thyreoary tzenoidea) ; between which the ventri culi laryugis are formed. The epiglottis does not exist in most of the bat kind : and in some mouse-like animals, as the rell-mouse (glis esctilentus,) it is hardly discernible. The superior ligamenta &Wills, as well as the ventriculi laryngis, are wanting in some bisulca, as the" ox and sheep.
Some species of mammalia have a pe culiar and characteristic voice; or at least certain tones, which are formed by additional organs. Of this kind are cer. taro tense membranes in some animals; and in others peculiar cavities, opening into the larynx, and sometimes appear ing as continuations of the ventriculi la ryngis.
The neighing of the horse, for ex ample, is effected by a delicate and nearly falciform membrane, which is at tached by its middle to the thyroid car tilage, and has its extremities running along the external margins of the rims glottidis.
The peculiar sound uttered by the ass is produced by means of a similar mem brane, under which there is an excava tion in the thyroid cartilage. There are moreover two large membranous sacs openng into the larynx.
The mule does not neigh like the mare by which it was conceived, but brays like the ass which begot it. It possesses exactly the same larynx as the latter, without any of the peculiar vocal organs of the mother ; a fact which, like many others, cannot be at all reconciled with the supposed pre-existence of previous ly formed germs in the ovarium of the mother.
Several apes and baboons, as also the rein-deer, have on the front of the neck large single or double laryngeal sacs, of various forms and divisions, communicat ing with the larynx by one or two open ings between the os hyoides and thyroid cartilage.
Some of the cercopitheci, as the C. Se niculos, and beelzebub, have the middle and anterior part of the os hyoides formed into a spherical bony cavity, by which the animals are enabled to pro duce those terrific and penetrating tones, which can be heard at vast distances, and have gained them the name of the howl ing apes.
The most striking peculiarity in the vocal organs of birds, and which be longs to all birds, with very few excep tions, consists in their possessing what is commonly called a double larynx, but which might be more properly de scribed as a larynx divided into two parts, placed at the upper and lower ends of the trachea. They have also two rim glottidis.
The superior, or proper rims glottidis, is placed at the upper end of the tra chea; but is not furnished with an epi glottis. The apparent want of this organ is compensated in several cases by the conical papilla placed at both sides of the rims.
The apparatus which is chiefly con cerned in forming the voice of birds is found in the inferior or bronchial larynx. This contains a second rima glottidis, formed by tense membranes, which may be compared in several cases, particular ly among the aquatic birds, to the reed at the mouth of musical instruments. It is furnished externally with certain pairs of muscles; varying in number in the diffe rent orders and genera; and with a kind of thyroid gland. The course and pro portionate length of the trachea, and particularly the structure of the inferior larynx, vary very considerably in the different species, and even in the two sexes, especially among the aquatic birds. Thus, fur example, the tame or dumb swan (alias olor) has a straight trachea ; whilst in the male of the wild, or whist ling swan (cygnus), this tube makes a large convolution, which is contained in the hollow of the sternum. In the spoon bill (Platalea leucorodia), as also in the Phasianus motmot, and others, similar windings of the trachea are found, not en closed in the sternum. The males of the two genera, arras and mergus, have at their inferior or bronchial larynx a bony cavity, which contributes to strengthen their voice.
A . very little comparison of the me chanism of wind musical instruments with the organs of the voice in birds, will spew how nearly they are allied to each other; and it may be observed, that the sound produced by some of the larger birds is exactly similar to the notes that proceed from a clarionet or hautboy in the hands of an untutored musician. The inferior glottis exactly corresponds to the reed, and produces the tone or simple sound. The superior larynx gives it ut terance, as the holes of the instrument ; but the strength and body of the note de pend upon the extent and capacity of the trachea, and the hardness and elasticity of its parts. The convolution and bony cells of the windpipe, therefore, may be com pared with the turns of a French horn, and the divisions of a bassoon ; and they produce the proper effects of these parts in the voices of those birds in which they are found.