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years to bring forth any results." Thanks to German students, the anatomy is clear, and, if we accept the theory of Helmholtz, the physiology is approximately so.
Prof. Burnett* has done the English-speaking student admirable service. He has given exact information in this difficult field of research in a clear manner, condensing the mass of material, and making deductions which seem free from bias.
STRUCTURE OF THE EAR.
In order to treat the subject clearly, I shall first revert briefly to the anatomy and physiology of the ear, Eustachian tube and naso-pharyngeal region. I will endeavor to direct attention to such points as will recall to the student those which may have been dropped out of memory, but which will bear repeating with profit. Let us appreciate, in all its bearings in this study "that anatomy is the foundation of all medical knowledge."
The middle ear or tympanum is an irregular, narrow cavity, situated within the petrous bone, between the external auditory canal and the outer wall of the labyrinth, having an oblique direction inward and outward, wedge-shaped, being narrow below and in front, and broad above and behind, its longest diameter from before backward being from six to nine lines, its diameter vertically about three lines, and its transverse diameter about two or three lines. Its cavity presents six faces or sides: 1. The superior wall, which is formed by a layer of bone, separating this cavity from that of the cerebrum, and through which bone-diseases of the tympanum advance, when they affect the brain. 2. The inferior wall, which presents a fissure or slit, about a line in length, called the Gasserian fissure. 3. The external wall, formed principally by the membrana tympani. 4. The internal wall, which has a vertical direction, and looks outwardly; it presents a uniform opening, which leads from the tympanum into the vestibule, called fenestra ovalis. Above this fenestra is the aqueduct of Fallopius, which gives passage to the facial portion
*The Ear: Its Anatomy, Physiology and Diseases. By CHARLES H. BURNETT, A. M., M. D. Aural Surgeon, Philadelphia; Henry C. Lee, 1877.
of the seventh pair of nerves. 5. The anterior wall is wider above than below, and presents the internal tympanic orifice of the Eustachian tube. 6. The posterior wall is also wider above than below, and presents an opening of communication with the mastoid cells. At the upper part of the posterior wall is a large, irregular sinus, and sometimes several small apertures, which lead into canals which communicate with. the interior of the mastoid process. This process contains in its interior an infinite number of compartments, which are termed the mastoid cells, and which are covered by a very delicate mucous membrane continuous with that lining the cavity of the tympanum. It will, therefore, be readily inferred that as these cells communicate freely with the tympanic cavity, inflammation attacking this cavity may extend to or exert an unfavorable influence upon them. The mastoid cells vary much in size and depth in different persons. In the early years of childhood the only representation of the mastoid cells is that horizontal position lying immediately adjacent to the tympanic cavity. It is well to remember this, for it is easy to be seen that diseases occurring in early childhood extend in a direction entirely different from those in later years. As the cells increase in size and number, with increasing years, they extend downward and backward into. the region of the cerebellum and lateral sinuses. Thus it is that caries, phlebitis and abscesses are found in this region, and present an entirely different train of symptoms to those occurring in childhood. This is a very important point in diagnosis and treatment.
The tympanic cavity of the ear, from the membrana tympani to the fenestra ovalis, is traversed by a chain of movable minute bones (ossicles of the tympanum), which articulate with each other by means of a little synovial and ligamentous apparatus.
The membrana tympani, or drum-membrane, separates the inner extremity of the external auditory canal from the cavity of the tympanum; it is a dry, thin, semi-transparent membrane, irregularly oval; and varies from nearly circular to elliptical, according to the age of the person. It is rather broader above
than below, and directed from above very obliquely downward and inward; its degree of obliquity also varies with age, and it assumes a more horizontal direction with very young persons. Its long or obliquely-vertical diameter is about twofifths of an inch; its circumference is thick, firm, somewhat denser and whiter than the rest of the membrane, and is inserted in a well-marked groove upon an elevated ridge at the tympanal margin of the bony meatus, in a manner somewhat resembling the setting of a crystal in the besil of a watch. Internally, where it forms a point of attachment with the chain of ossicles, the membrana tympana is convex; externally, where it terminates the external auditory canal, it is concave. It is composed of four extremely thin layers, and is highly sensitive. Its office is to receive and convey sounds to the ossicles, and thence to the labyrinth; and as a guard to the delicate structures of the middle ear; and to modify the influence of loud sounds; and to render the ear more susceptible to the influence of delicate ones.
The tympanal walls being everywhere invested by a membrane which possesses the double character of a mucous and periosteal membrane, the inflammatory process (as in catarrh of the middle ear, which gives rise, in its congestive or forming stage, to most of the earaches experienced in childhood) is attended by an abundant secretion and is characterised by its extreme painfulness. The sensitiveness of this structure is very great. That it is wonderfully provided with sensory nerves will be observed by the following summary of those which compose the tympanic plexus, and its sympathetic relations are shown in that it (the plexus) derives supplies from sources most extensive: thus by means of branches from the otic ganglion the inferior maxillary nerve is brought into intimate relations with it, and the petrosal ganglion of the glosso-pharyngeal nerve supplies the tympanic branch, or Jacobson's nerve, which constitutes a large portion of this anastomosis. The carotid plexus of the sympathetic sends a branch to the glosso-pharyngeal and thus establishes a communication between the ear and the superior cervical ganglion of the sympathetic nerve. Through Meckel's
ganglion by means of the Vidian nerve the superior maxillary of the fifth pair of nerves also is connected with the tympanic system. Besides these there are other connections. This structure is also richly supplied with blood-vessels. In describing these parts Burnett calls attention to the importance of bearing "these relations in mind when considering certain neuralgias in and about the ear, which might otherwise be puzzling." In a very large number of diseases of the ear the causes are to be sought elsewhere than in the hearing organ itself, since they will depend, for the most part, on the nervous sympathy; the most prominent of these causes in children, are dentition, dental caries and "colds" in the head.
Hence, in all affections of this organ, where no sufficient local influences can be found, it is well to cast about and endeavor to discover any sources of reflex irritation, since treatment directed to the remote origin of the difficulty will be found the most effective; thus a remedy applied to a carious tooth may cure an otalgia, a reversal of the practice of the ancients, who made application to the ear for the relief of toothache.
The internal ear, or labyrinth, is situated in the petrous portion of the temporal bone, between the tympanic cavity and the internal auditory canal; it is very complicated in its form; it commences at the fenestra ovalis and consists of the three following parts: 1. The vestibule. 2. The semi-circular canals. 3. The cochlea.* A very fine fibro-serous membrane lines all the cavities of the labyrinth, the internal surface which secretes the liquor Cotunni, and which liquor exactly fills all the labyrinthian cavities in which we find neither air nor emptiness. The internal ear, then, consists of a chamber with two windows and lateral galleries, enclosed in walls of solid bone; within these walls are included sacs filled with fluid contents, these sacs floating in fluids which completely fill the chambers and galleries; within these sacs resting upon the inner lining as a base are the terminal filaments of the
*See Chronic Diseases, by Prof. JOHN KING, page 1193, for a very excellent and minute description of the labyrinth.
auditory nerve. Immediately in relation with these nervefilaments are arterial and nervous radicles, upon which the entire structure depends for nutrition. Notice this summary: bony walls enclosing fluid contents in which are suspended membranous sacs containing fluids in which float fine nervefilaments; all these so delicately adjusted that any motion in any part of the mechanism causes like motion throughout the whole.
The function of this mechanism is simple; any application of force which acts upon the closed windows of this bony chamber causes waves through the fluids. In the normal ear the tension of these fluids is uniform, and the terminal nervefilaments are adjusted or tuned to correspond to this uniform tension. It will, therefore, be readily seen that any factor that comes in to change the normal condition will cause a change of tension, and result in abnormal phenomena. It is not necessary to enter further into the anatomy and physiology of the internal ear. I would simply say: sound implies two things; waves or undulations, and a nerve of hearing. Hearing is the mental act consequent upon perception of sound-waves by the labyrinth, and their conduction to the brain by the auditory nerve. The theory which is generally accepted by physiologists in explanation of this point is the one given by Prof. Helmholtz, and called in honor of that distinguished physicist, "the Helmholtz theory of hearing."*
The Eustachian tube, the pivotal point of this study, is a somewhat trumpet-shaped canal from an inch and a half to two inches in length, through which a communication is kept up between the tympanum and the cavity of the fauces; its small extremity, or intratympanic orifice opens into the cavity of the tympanum, from which it proceeds, gradually increasing in diameter, obliquely downward, inward and forward to the superior and lateral part of the pharynx. Its faucial orifice is fibro-cartilaginous, larger than at any other part of the canal, bell- or funnel-shaped, and will admit the introduction of a medium-sized bougie, while a very fine bristle
*The essential points of Helmholtz' theory will be found in an abstract by A. H. BUCK, M. D., in his treatise on the EAR, 1880, p. 12.