[Introduction to Chapter 8]
The following page will set forth the legend of this figure.
|A, A||Portion of the foramen [meatus acusticus externus] that extends from the ear inward to the the membrane marked B.|
|B||Membrane [membrana tympanica] drawn across the foramen that leads from the ear into the cavity [cavitas tympanica] carved in the temporal bone for the organ of hearing.|
|C||One ossicle of the organ of hearing, resembling a little hammer [malleus].|
|D||Nerve of the fifth pair of cerebral nerves [nervi craniales]. 1|
|E||Branch of the fifth pair of cerebral nerves, branched off through a blind foramen to the principal temporal muscle. 2|
|F||Branch of the fifth pair of cerebral nerves, passing through the foramen in which the vein is received that leads to the organ of hearing.|
|G||Group belonging to the nerve of the fifth pair at the level, smooth part of the cavity [cavitas tympanica] hollowed out here for the organ of hearing.|
|H||Spherical area, to whose anterior surface the second ossicle of the organ of hearing is attached. Marked I here, it [incus] is comparable to an anvil or molar.|
|K, K||Small cavities [cellulae mastoideae], with which the inside of the cavity provided for the organ of hearing abounds.|
|L||Anterior aspect of the malleus freed of its surrounding parts.|
|M||Posterior aspect of the malleus similarly freed.|
|N||Anterior aspect of the anvil [incus] or molar-like bone, free of other parts.|
|O||Posterior aspect of the anvil or molar-like bone, free of other parts.|
|P||Anterior aspect of the anvil and malleus, as they are joined in the ear.|
|Q||Posterior aspect of the joined anvil and malleus.|
The cavity made for the organ of hearing, and the foramina extending
When I describe the construction of the organ of hearing, you will hear that a large and winding cavity is carved in the temporal bone leading via a twisted foramen [meatus acusticus internus] into the brain cavity of the skull. And by another much larger and less twisted foramen [meatus acusticus externus], it extends toward the outer surface of the head, to the ear. Then from this cavity two other foramina are extended, of which one will be called the blind foramen [canalis facialis] the other could also be so called, but unlike the former it is twisted and narrow, and provides a path [sulcus sinus petrosi superioris] to the vein (n in chapter 14, book 3) coming in to nourish the organ of hearing. These foramina (a, a, b, c in chapter 12) will be described with their own figure legend in the twelfth chapter, but now we mention only those we consider relevant to an account of the ossicles.
Nerves from the fifth pair to the organ of hearing
The second nerve (D) [nervus vestibulocochlearis] of the fifth pair of cerebral nerves enters up into the foramen [meatus acusticus internus] facing the space where the brain is contained, and except for branches (E, F) running off from it through the narrower and thinner foramina [porus acusticus internus], with its greater portion (G; see also a, b, c, f of figs. 1 and 2, chapter 2, book 3) it covers like a membrane [labyrinthus membranaceus] the cavity cut into the temporal bone—not all of the cavity, but only certain parts, as if that portion of the nerve were divided into several membranes covering some regions of this cavity. Among the remaining areas of this cavity, which vary and are flat in one place and in another porous [paries mastoideus] like fine sponge or pumice, one is spherical and smooth (H), hedged off by a slightly swelling bony circle [promontorium?].
The anvil-like ossicle
At the outside of this circle enclosed by the nerve of the fifth pair and nearest the ear [auris externa], an ossicle (I, N, O) is seen that is affixed to this bony circle by two thin, sharp processes like legs [crus longum, crus breve]; above, where its legs meet, it is made thicker and heavier, like an anvil. 4 This is the second ossicle of the organ of hearing, which I am accustomed to show during dissection with considerably less difficulty than I can describe it here,
The ossicle that is not unlike a small hammer
The second ossicle (C, L, M) involved in the fabric of the organ of hearing is quite different from the one just described, and it attaches to another membrane. A foramen [meatus acusticus externus] in the cavity or hollow cut in the temporal bone, facing the ear [auris externa] in that part where it is near the space of the cavity [cavitas tympanica], is covered by an extremely thin, quite translucent small membrane (B) [membrana tympanica] in the same way that we say a vessel is covered or sealed by its base. The ossicle 7 is transversely attached to this membrane and transversely laid upon it inside, just as in drums we see one string and another heavier one stretched across the membrane. 8 In order to be more firmly braced, the ossicle has a long, thin process [manubrium mallei], by which it is attached along its width to the membrane.
Comparison of the second ossicle to the femoral bone
This process might be compared to the part of the femur (figs. in ch. 30) that extends from the processes we call rotators 9 to the lower heads [condylus medialis, condylus lateralis] of the femur; indeed, if you imagine these lower heads cut away from the rest of the femur, the whole ossicle would look just like it. For as the femur has two processes [trochanter major, trochanter minor] near its neck, this ossicle has some small processes [p. anterior, p. lateralis] in the same place by which it is more firmly attached to its membrane [membrana tympanica]. Then, as the neck of the femoral bone slopes obliquely toward the inside of the body near the socket [acetabulum] of the hip bone and comes to an end at a perfectly round head [caput femoris], so this ossicle turns inward away from the membrane and ends in a round head [caput mallei] which is smooth and not at all rough, and is joined (P, Q) [articulatio mallearis] by very thin membranes [capsula articularis] to the upper part [corpus incudis] of the other ossicle [incus] that we compared to an anvil or molar, like a hammer loosely attached to an anvil: no differently than if one ossicle just mentioned were working as a little hammer and the other an anvil, but much too small in proportion to the size of the malleus.
The use of ossicles of the organ of hearing
Whether the incus and the malleus function as their shapes suggest, and the second ossicle [malleus] is moved by the slightest breath (as it is in dissection) along with the membrane to which it is attached, while the first ossicle remains more or less at rest, I would not want to say, because I do not understand the mechanics of hearing as well as I would like. This is not because I am unaware of that common refuge of medical experts to the mixture of parts 10 and the circles of air; we are all persuaded by the fall of pebbles into water that these waves are carried into the ear from an impact upon the air, and that they strike a certain membrane: but at the same time we are completely ignorant about the construction of this organ. 11 The Maker of things devises things here with his clever artifice that are far too divine, whose structure I demonstrate clearly enough in classes, but whose use and way of working I can explain no better than I can the eye itself. But because much more will be said later about the organ of hearing, it has sufficed here to have described the ossicles. If you have not followed this account, put on the table the head of a calf, lamb, or some other animal, divide the bone of the temples in both directions, and study the construction of these bones. 12 It is much better to examine them in a raw head than in one that has been boiled, and rather in a human than in any other animal. For by the former procedure you will not only encounter a construction of ossicles that is extremely pleasant to view, you will also marvel that the way nearly all musical instruments are made is taken from the structure of the organ of hearing.
Marcus Antonius Genua and Wolfgang Hervort, chiefly responsible for
my undertaking and completion of this work
It is chiefly for this reason that Marcus Antonius Genua 13 is accustomed to contemplate the harmony of the organ of hearing with the greatest pleasure. Not only is this man the most consummate of musicians but also the special glory of the philosophers of our time, an eminent person and a professor of philosophy, the most learned among the Paduans in a variety of disciplines, to whom students of science will owe as much as they will gain from this effort of mine, since he first inspired me to begin this work, and has been no less my eager counsellor than the rare model of virtue Wolfgang Herwort, 14 a patrician of Augsburg, because of his incredible goodwill toward letters and scholars; most worthy of immortality, and special object of my devotion while I live because he has left nothing undone within his powers for the completion of this work.
Appendix: 1555 version of the first 32 lines of the chapter 8
narrative (see note 6 above)
Although in the seventh book we shall deal at length with the structure of the instrument of hearing along with the other sensory organs, this structure must now be described in passing because of certain ossicles which it contains, lest by reserving them entirely until the seventh book we seem to have passed them over in an otherwise comprehensive account of the bones. It is conjectured that neither Galen nor any other before him had seen these ossicles — and several others besides — from the fact that no mention of them is ever made. A large and quite irregular cavity (in the principal illustration, and in the penultimate text figure of ch. 12) is carved in the temporal bone, with four foramina coming out from it. The first of these [meatus acusticus externus] (a in fig. 3, ch. 12) is wide but circuitous, on each side admitting the nerve 15 (a in figs. 1, 2, ch. 2 bk. 4) of the fifth pair of cerebral nerves into the region of the head where the cerebrum is contained. The second foramen [meatus acusticus internus] (a in fig. 3, ch. 12), shorter but much wider than the one just mentioned, runs to the ear. The third [f. stylomastoideum] (b in fig. 2, ch. 12) is narrow and variously twined; it is called the blind foramen, as we shall explain later, and transmits a branch (c in figs. 1, 2, ch. 2 bk. 4) of the nerve [n. facialis] of the fifth pair. The fourth [tuba auditoria, pars ossea] (V in fig. 2, ch. 12) is somewhat wider than the preceding one, and not as twisted. Proceeding forward as the former had backward past another branch [n. vestibulocochlearis?] (b in figs. 1, 2, ch. 2 bk. 4) of the the nerve of the fifth pair, to which it provides a passage, it transmits a vein [?] (n in the figure illustrating ch 14, bk. 3) that goes to the organ of hearing. But the nerve of the fifth pair is not entirely absorbed into those two branches: a larger portion [organum vestibulocochleare] (F in figs. 1, 2, bk. 4) of it surrounds and covers the cavity [c. tympanica] incised in the temporal bone somewhat like a membrane — not indeed the entire cavity but some surfaces of it, as if the larger portion of a nerve were divided into several membranes covering numerous regions of the cavity. Among the other surfaces of the cavity, some of which are flat and smooth and some porous like open pumice and sponge and irregular with considerable variation, one area (H) is round and smooth, surrounded by a bony circle that protrudes like a line. This is covered by a special portion (G) of the fifth nerve 16 as if by a small membrane. Near the outside of this circle, closest to the region of the ear, is placed an ossicle (I, N, O) braced and stabilized by two thin, sharp processes or legs; 17 the outer of these, nearer the ear, is shorter, thicker, and wider, and it ends in a sharp point.