CHAMBERS'S INFORMATION FOR THE PEOPLE. 



by a partition, partly bony, partly membranous. 

 The upper portion communicates with the vesti- 

 bule, and, from its fancied resemblance to a 

 stair, has been called scala vestibuli. Suppose we 

 ascended this stair to the apex of the cochlea, we 

 would there find a small opening communicating 

 with the lower compartment, which has been called 

 the scala tympani. It received this name because 

 at the bottom it communicates with the tympanum 

 by a round opening, called the fenestra rotunda, 

 closed by a thin membrane. The cochlear branch 

 of the auditory nerve enters the base of the pillar 

 just mentioned, and distributes branches to the 

 membranous portion of the scalae. But this is not 

 all. Between the two scalae or staircases, in a 

 triangular space, there is a remarkable organ, 

 called the Organ of Corti. This is a com- 

 plicated anatomical structure, which space will 

 not allow us fully to describe here, but essentially 

 it consists of three or four thousand jointed rods, 

 apparently capable of vibrating, and presenting, 

 when viewed from above, an appearance some- 

 what like the key-board of a piano. 



\Ve know little regarding the functions of the 

 different parts of the internal ear. That they have 

 different functions, we infer from the structure 

 being so dissimilar, and also from the facts of 

 comparative anatomy. In the animal kingdom, 

 the vestibule first appears ; to this are superadded 

 the semicircular canals ; and lastly, the cochlea, 

 which increases in complexity from the lower 

 orders of the mammalia up to man, in whom it 

 is one of the most complicated organs of the body. 

 The vestibule probably enables us to experience 

 a sensation of sound as such ; the semicircular 

 canals may, as suggested by Wheatstone, assist in 

 determining the direction of sounds ; while there 

 are many arguments in favour of the view, that 

 the cochlea, as we find it in man, with a highly 

 elaborated organ of Corti, may be the mechanism 

 by which we appreciate musical sounds, which 

 act so powerfully in exciting the emotions. 



The range of hearing, like that of vision, varies 

 in different persons. Some are insensible to 

 sounds that others hear. Many cannot hear the 

 chirp of a grasshopper or the squeak of a bat, 

 two of the shrillest sounds in nature. The range 

 of the ear is much greater than that of the eye 

 in detecting movements which produce vibrations. 

 Thus we hear the sound produced by a vibrating 

 rod or string long after we have ceased to see the 

 movements. The range of the human ear is 

 probably nine or ten octaves. 



The Muscular Sense. There is still another 

 sense, called the muscular sense, or sense of 

 weight. If we close our eyes, and hold a weight 

 on the palm of the outstretched hand, we ex- 

 perience a peculiar sensation. It is not referable 

 to any of the five senses, except, perhaps, to touch. 

 But it is not simple touch. We are conscious of 

 an effort to sustain the weight, and of a firm con- 

 in 



dition of the muscles of the arm. This sensation 

 is the muscular sense. It is the sensation we 

 experience when any groups of the voluntary 

 muscles are called into action, and by it we 

 become aware of the condition of these muscles. 

 By means of this sense, we stand erect, we walk, 

 balance ourselves on a narrow ledge, throw stones 

 or weapons, play on many instruments, &c. ; and 

 it adds largely to our feelings of pleasure. 



VOICE AND SPEECH. 



There is a great difference between voice and 

 speech. Voice is produced by vibrations of two 

 thin folds of membrane called the vocal cords, 

 placed in the larynx, at the top of the trachea or 

 windpipe : speech is the modification of voice 

 into sounds connected with certain ideas produced 

 by the action of the brain, which we wish to com- 

 municate to our fellow-men. Many animals hare 

 voice ; none, except man, have articulate speech 

 expressive of ideas. The organ of voice is the 

 larynx (behind the Pomum Adamt), the struc- 

 ture of which is very complicated, and cannot 

 be here described. It consists of various car- 

 tilages and muscles, the object of which is to 

 tighten or relax the margins of two folds of mem- 

 brane, called the vocal cords. By the vibrations 

 of these cords voice is produced, and by tightening 

 or relaxing, separating or approximating them, 

 we obtain various modifications of voice. When 

 a high note is sounded, the cords are tense and 

 close together; and, on the contrary, when we sing 

 a deep bass note, they are relaxed and wide apart. 

 The quality and compass of the voice differ in 

 individuals. In men, the highest is the tenor ; the 

 lowest, the bass ; the intermediate, the barytone. 

 In women, the corresponding notes are the 

 soprano, the contralto, and the mezzo-soprano. 

 The difference between the deep bass of a man 

 and the shrill soprano of a woman, is, that in the 

 man the cords are longer and less tense than in 

 the woman. 



Speech is voice so modified by the action of the 

 throat, tongue, cheeks, and lips, as to mean or 

 indicate objects, properties, ideas, &c. This is 

 language. If we breathe quietly, without causing 

 the vocal cords to vibrate, and modify by the 

 action of the mouth, &c. the volume of air ex- 

 pelled, we produce whispering. 



III. FUNCTION OF REPRODUCTION. 



The third great function of animal life is repro- 

 duction, by which the species is perpetuated. It 

 is beyond the scope of this article to treat of this 

 subject, and reference is accordingly made to 

 special works on Anatomy and Physiology. 



