the cartilages are harder, and are sometimes almost completely ossified. The loudness of the voice depends in part upon the force with which the air is expelled from the lungs; but the variations in this respect which exist among different individuals, seem partly due to the degree in which its resonance is increased by the vibration of the other parts of the larynx, and of the neighboring cavities. In the Howling Monkeys of America, there are several pouches opening from the larynx, which seem destined to increase the volume of tone that issues from it;-one of these is excavated in the substance of the hyoid bone itself. Although these Monkeys are of inconsiderable size, yet their voices are louder than the roaring of lions, and are distinctly audible at the distance of two miles; and when a number of them are congregated together, the effect is terrific.

980. The vocal sounds produced by the action of the larynx are of very different characters; and may be distinguished into the cry, the song, and the ordinary or acquired voice. The cry is generally a sharp sound, having little modulation or accuracy of pitch, and being usually disagreeable in its timbre or quality. It is that by which animals express their unpleasing emotions, especially pain or terror; and the Human infant, like many of the lower animals, can utter no other sound. In song, by the regulation of the vocal cords, definite and sustained musical tones are produced, which can be changed or modulated at the will of the individual. Different species of Birds have their respective songs; which are partly instinctive, and partly acquired by education. In Man, the power of song is entirely acquired; but some individuals possess a much greater facility in acquiring it than others, -this superiority appearing to depend upon their more precise conception of the tones to be sounded, as well as their more ready imitation, -besides differences in the construction of the larynx itself. The larynx of an accomplished vocalist, obedient to the expression of the emotions, as well as to the dictates of the will, may be said to be the most perfect musical instrument ever constructed.-The voice is a sound more resembling the cry, in regard to the absence of any sustained musical tone; but it differs from the cry, both in the quality of its tone, and in the modulation of which it is capable by the will. In ordinary conversation, the voice passes through a great variety of musical tones, in the course of a single sentence, or even a single word, sliding imperceptibly from one to another; and it is when we attempt to fix it definitely to a certain pitch, that we change it from the speaking to the singing tone.

981. The power of producing articulate sounds, from the combination of which Speech results, is altogether independent of the Larynx; being due to the action of the muscles of the mouth, tongue and palate. Distinctly-articulate sounds may be produced without any vocal or laryngeal tone, as when we whisper; and it has been experimentally shown, that the only condition necessary for this mode of speech is the propulsion of a current of air through the mouth, from back to front. On the other hand, we may have the most perfect laryngeal tone without any articulation; as in the production of musical sounds, not connected with words. But in ordinary speech, the laryngeal tone is modified by

the various organs which intervene between the larynx and the os externum. The simplest of these modifications is that by which the Vowel sounds are produced, these sounds being continuous tones, modified by the form of the aperture through which they pass out. Thus, let the reader open his mouth to the widest dimensions, depress the tongue, and raise the velum palati, so as to make the exit of air as free as possible; on then making a vocal sound, he will find that this has the character of the vowel a in ah. On the other hand, if he draw together the lips, still keeping the tongue depressed, he will pass to the sound represented in the English language by oo, in the Continental languages by u. By attention to the production of other vowel sounds, it will be found that they are capable of being formed by similar modifications in the form of the buccal cavity and the size of the buccal orifice; and that they are capable of being sustained for any length of time. There is an exception, however, in regard to the sound of the English i, as in fine, which is, in reality, a diphthongal sound, produced in the act of transition from a peculiar indefinite murmur to the sound of the long e, which takes its place when we attempt to continue it. The short vowel sounds, moreover, such as a in fat, e in met, o in pot, &c., are not capable of being perfectly prolonged, as they require, for their true enunciation, to be immediately followed by a consonant.-A tolerably good artificial imitation of Vowel sounds has been effected by means of a reed-pipe representing the larynx, surmounted by an Indiarubber ball, with an orifice, representing the cavity and orifice of the mouth. By modifying the form of the ball, the different vowels could be sounded during the action of the reed.

982. In the production of the sounds termed Consonants, the breath suffers a more or less complete interruption, in its passage through the parts anterior to the larynx. The most natural primary division of these sounds is into those which require a total stoppage of the breath at the moment previous to their being pronounced, and which, therefore, cannot be prolonged; and those in pronouncing which the interruption is partial, and which can, like the vowel sounds, be prolonged ad libitum. The former have received the designation of explosive consonants; the latter are termed continuous. In pronouncing any consonants of the explosive class, the posterior nares are completely closed; and the whole current of air is directed through the mouth. This may be checked by the approximation of the lips, as in pronouncing b and p; by the approximation of the point of the tongue to the front of the palate, as in pronouncing d and t; or by the approximation of the middle of the tongue to the arch of the palate, as in pronouncing the hard g or k. The difference between b, d, and g, on the one hand, and p, t, and k, on the other, depends simply upon the greater extent of the meeting surfaces in the former case than in the latter. In sounding some of the continuous consonants, the air is not allowed to pass through the nose; but the interruption in the mouth is incomplete; this is the case with v and f, 8 and 2. In others, the posterior nares are not closed, and the air has a nearly free passage, either through the nose alone, as in m and n, or through the nose and mouth conjointly, as in l and r. The sound of h is a mere aspiration, caused by an increased force of breath; and that

of the guttural ch, as it exists in Welsh, Gaelic, and most Continental languages, is an aspiration modified by the elevation of the tongue, which causes a slight obstruction to the air, and an increased resonance in the back of the mouth.

983. The study of the mode in which the different Consonants are produced, is of particular importance to those who labor under defective speech, especially that difficulty which is known as Stammering. This very annoying impediment is occasioned by a want of proper control over the muscles concerned in Articulation; which, instead of obeying the Will, are sometimes affected with an involuntary or spasmodic action, that interrupts the pronunciation of particular words,— just as, in Chorea, the muscles of the limbs are interrupted by spasmodic twitchings, in the performance of any voluntary movement. In fact, persons affected with general Chorea frequently stammer; showing that ordinary Stammering may be considered as a kind of local Chorea. The analogy between the two states is further indicated by the corresponding influence of excited Emotions in aggravating both.

It is in the pronunciation of the consonants of the explosive class, that the stammerer usually experiences the greatest difficulty; for the total interruption to the breath, which they occasion, is frequently continued involuntarily ;* so that either the expiration is entirely checked, the whole frame being frequently thrown into the most distressing semiconvulsive movements, or the sound comes out in jerks. Sometimes, however, the spasmodic action occurs in the pronunciation of vowels and continuous consonants; the stammerer prolonging his expiration, without being able to check it.

984. The best method of curing this defect (where there is no malformation of the organs of speech, but merely a want of power to use them aright), is to study the particular difficulty under which the individual labors; and then to cause him to practise systematically the various movements concerned in the production of the sounds in question, at first separately, and afterwards in combination,-until he feels that his voluntary control over the muscles is complete. The patient would at first do well to practise sentences, from which the explosive consonants are omitted; his chief difficulty, arising from the spasmodic suspension of the expiratory movement, being thus avoided. Having mastered these, he may pass on to others, in which the difficult letters are sparingly introduced; and may finally accustom himself to the use of ordinary language. One of the chief points to be aimed at, is to make the patient feel that he has command over his muscles of articulation; and this is best done, by gradually leading him from that which he can do, to that which he fears to attempt.

The interruption of the expiratory movement in Stammering, is usually stated to take place in the glottis; but the Author is satisfied that, in all ordinary cases at least, it is in that condition of the mouth, which is preparatory to the pronunciation of one of the explosive consonants.

INDEX.

N.B. The numbers refer to the Paragraphs.

ration in, 657-661; nervous system in, Carbonic acid, decomposition of, by Plants,

Corpuscles of blood, red, 215-223; white, 214. Epilepsy, 886.

Crustacea, geographical distribution of, 133; Excreting processes, general review of, 731-