Tympanic bulla

“ As the hind foot elongates the index will increase; elongation of the hind foot is interpreted as a specialization.
The Cranial index (breadth across bullae/length of the skull × 100) reflects the degree of development of the tympanic or mastoid region, or both, and is thought to be an adaptation for more acute hearing and possibly for more delicate balance. Inflation of the tympanic bullae is thought to be a specialization. As the auditory bullae become more inflated, the index increases toward 100. ”

“ The auditory bulla and the tympanic are divided by an internal partition. The paroccipital process is separate from, or only extends to a slight degree upon the auditory bulla. The thoracic vertebrae number 13; the feet are digitigrade, with five front and four hind toes, of which the claws are retractile; and the metatarsus is haired all round. Anal glands are present.
As regards the teeth, when considered in more detail, the incisors are small, and the canines large, strong, slightly recurved, with trenchant edges and sharp points, and placed wide apart. ”

“ The lachrymal (fig. 96, 15) is small and lies almost entirely inside the orbit. The anterior narial aperture (fig. 97, 8) is wide and directed upwards, opening high on the anterior surface of the skull. It is bounded above by the short thick nasals and below by the premaxillae. The narial passage is freely open, maxillo-turbinals not being developed. The palatine is well developed, the pterygoid is small and early fuses with the pterygoid process of the alisphenoid. The tympanic is united with the periotic but not with the squamosal, and forms a large auditory [476] bulla. ”

“ Exception must again be made for the anteroposterior diameter of the inner lobe of the last upper molar which is less in females, and only slightly more in males. In males of invicta the tympanic bullae are longer in relation to the basilar length. ”

“ This effort partially exhausts the space behind the tympanic membrane, which is then thrown into a state of tension by the pressure of the outward air. A similar deafness to low sounds is produced when the nose and mouth are stopped, and a strong effort is made to expire. In this case air is forced through the Eustachian tube into the drum of the ear, the tympanic membrane being distended by the pressure of the internal air. The experiment may be made in a railway carriage, when the low rumble will vanish or be greatly enfeebled, while the sharper sounds are heard with undiminished intensity. ”

“ The roof is formed by a very thin plate of bone, called the tegmen tympani, which separates the cavity from the middle fossa of the skull. Below the roof the upper part of the tympanum is somewhat constricted off from the rest, and to this part the term “attic” is often applied. The floor is a mere groove formed by the meeting of the external and internal walls. The outer wall is largely occupied by the tympanic membrane (fig. 1, o) , which entirely separates the middle ear from the external auditory meatus ”

“ To produce a musical tone we must have a body which vibrates with the unerring regularity of the pendulum, but which can impart much sharper and quicker shocks to the air.
Imagine the first of a series of pulses following each other at regular intervals, impinging upon the tympanic membrane. It is shaken by the shock; and a body once shaken cannot come instantaneously to rest. The human ear, indeed, is so constructed that the sonorous motion vanishes with extreme rapidity, but its disappearance is not instantaneous ”

“ Hence a woman’s ordinary pitch in the lower sounds of conversation is more than an octave above a man’s; in the higher sounds it is two octaves.
And here it is important to note that by the term vibrations is meant complete ones; and by the term sonorous wave is meant a condensation and its associated rarefaction. By a vibration an excursion to and fro of the vibrating body is to be understood. Every wave generated by such a vibration bends the tympanic membrane once in and once out. These are the definitions of a vibration and of a sonorous wave employed in England and Germany. ”

“ Relative to the basilar length, the zygomatic breadth is more, the tympanic bullae are narrower, and the braincase is deeper at the anterior end of the basioccipital. The female is 41 per cent heavier than streatori, there being no overlap in most cranial and dental measurements. M1, however, is approximately the same size in each subspecies. ”

“ Noise affects us as an irregular succession of shocks. We are conscious while listening to it of a jolting and jarring of the auditory nerve, while a musical sound flows smoothly and without asperity or irregularity. How is this smoothness secured? By rendering the impulses received by the tympanic membrane perfectly periodic. A periodic motion is one that repeats itself. The motion of a common pendulum, for example, is periodic, but its vibrations are far too sluggish to excite sonorous waves. ”

“ In all the Amphibia, Sauropsida and Mammalia, except the Urodela and a few Anura and Reptilia, the first visceral or hyomandibular cleft enters into intimate relations with the organs of hearing, and from it and the adjoining parts are formed the tympanic cavity, the Eustachian tube, the tympanic membrane and the meatus auditorius externus. The tympanic membrane serves to receive from the air the sound vibrations, which are communicated to fluids contained in the true auditory labyrinth by one ossicle or by a chain of auditory ossicles. ”

“ The great object, therefore, of the after-treatment is to prevent the inner wall of the tympanic cavity becoming covered with granulations which may become organized later into a fibrous pad covering the inner wall of the tympanic cavity, and thus prevent movement of the stapes and, in consequence, marked deafness. The prevalent idea that the hearing power is destroyed irrevocably, as a result of the complete operation, is quite wrong: equally so is the harmful statement that, as a result of this operation, complete restoration of the hearing can be obtained. ”

“ The auditory nerve terminates in eight sense organs, which contain hair cells. There is no cochlea as in the mammalian ear. The assumption commonly made is that vibrations in the water or air by direct contact cause the tympanic membrane to vibrate; this in turn causes a movement of the columella, which is transmitted to the perilymphatic fluid of the inner ear. The sensory hair cells are disturbed by the movements of the otoliths in the endolymph, and thus an impulse is originated in the auditory nerve which results in a sensation more or less resembling our auditory sensation. ”

“ The external ear consists of an expanded portion known as the pinna or auricle, and of a passage, the auditory canal or meatus, leading inwards from it. The surface of the auricle is convoluted to collect and transmit the vibrations of air by which sound is produced the auditory canal conducts these vibrations to the tympanic membrane. Many animals move the auricle in the direction of the sound. Thus the horse pricks up its ears when it hears a noise, the better to judge of the direction of sounds. ”

“ The tympanic membrane is furthermore able to render sensible differences in the pressure of the external atmosphere, too slight to be felt either as noise or in this more violent way. If the reader will sit with closed eyes and let a friend approximate some solid object, like a large book, noiselessly to his face, he will immediately become aware of the object's presence and position—likewise of its departure. ”

“ The distress induced by exposure to loud noises is also accounted for by the fact that the comparative rigidity of the sound transmitting apparatus deprived the deeper sensitive portion of the ear of the protection normally afforded it by the elastic structure capable of taking up and dispersing the excessive impulse and by the further fact that the contraction of the tensor tympani muscle, which contraction is an almost invariable accompaniment of certain chronic diseases of the middle ear, served to still further impair the mobility of the drum-head and ossicles. ”

“ For the bodies which yield grave sounds are in general large, and consequently will make an impression upon the air by a large number of trembling particles.
Thirdly, all very loud noises are disagreeable. Now it is easy to conceive, that very violent agitations of the membrana tympani may produce the solution of continuity in the small medullary particles of the auditory nerve. An inflammation in the small vessels of the auditory nerve may render it so susceptible of violent vibrations, as to be hurt by gentle sounds, as sometimes happens in distempers ”

“ Such growths, provided they are pedunculated and do not abut on the tympanic membrane, can sometimes also be removed by the same method; much depends on their shape and situation. If sessile or too deeply placed, the operation may have to be completed by reflecting forward the auricle. Before terminating the operation a clear view of the tympanic membrane should always be obtained.
The meatus is finally syringed out with a 1 in 5,000 aqueous solution of biniodide of mercury and dried, a strip of sterilized gauze being inserted into the auditory canal. ”

“ The tympanum remains as a ring within an auditory bulla; the orbit is either surrounded by bone, or separated from the hinder part of the skull by a post-orbital process of the frontal; the upper molars have broad 5-cusped crowns with a W-shaped pattern; and the intestine is generally furnished with a caecum. ”

“ Sometimes water that gets in this way causes inflammation and cold, which hurt the sense of hearing. No one should ever strike another on the ear, even in play. It is likely to cause deafness. What is called the drum of the ear is a very delicate membrane which receives the sound. ”

“ A resonance absolutely non-vesicular is always tympanitic (Flint) . This tympanitic sound is so constant under the clavicle that although it may be from other causes, its appearance would lead us to suspect effusion, especially in children. It is not only at the apex, but wherever the lung shrinks from pleuritic exudation and loses in tension, the percussion sound has the tympanitic quality. We find it occasionally near the sternum, and sometimes in sacculated effusions we observe it in different parts of the thorax. Traube, and subsequently Fraentzel (Ziemssen's Cyc.) ”

“ With respect to the external ear in man, whether it is completely removed either by accident or design, deafness ensues, although its partial removal is not attended with this inconvenience: the external ear, therefore, or something in its form to collect sound, is a necessary part of the organ.
The next division is the intermediate ear; it consists of the tympanum, mastoid cells, and Eustachian tube. The tympanum contains four small delicate bones, viz. the malleus, the incus, the stapes, and the os orbiculare, joined to the incus. ”