Henry Gray (18251861). Anatomy of the Human Body. 1918.
A superior ligament of the incus (lig. incudis superius) has been described, but it is little more than a fold of mucous membrane.
The vestibular surface and the circumference of the base of the stapes are covered with hyaline cartilage; that encircling the base is attached to the margin of the fenestra vestibuli by a fibrous ring, the annular ligament of the base of the stapes (lig. annulare baseos stapedis).
The Muscles of the Tympanic Cavity (musculi ossiculorum auditus) are the Tensor tympani and Stapedius.
The Tensor tympani, the larger, is contained in the bony canal above the osseous portion of the auditory tube, from which it is separated by the septum canalis musculotubarii. It arises from the cartilaginous portion of the auditory tube and the adjoining part of the great wing of the sphenoid, as well as from the osseous canal in which it is contained. Passing backward through the canal, it ends in a slender tendon which enters the tympanic cavity, makes a sharp bend around the extremity of the septum, and is inserted into the manubrium of the malleus, near its root. It is supplied by a branch of the mandibular nerve through the otic ganglion.
FIG. 919 Chain of ossicles and their ligaments, seen from the front in a vertical, transverse section of the tympanum. (Testut.) (See enlarged image)
The Stapediusarises from the wall of a conical cavity, hollowed out of the interior of the pyramidal eminence; its tendon emerges from the orifice at the apex of the eminence, and, passing forward, is inserted into the posterior surface of the neck of the stapes. It is supplied by a branch of the facial nerve.
Actions.The Tensor tympani draws the tympanic membrane medialward, and thus increases its tension. The Stapedius pulls the head of the stapes backward and thus causes the base of the bone to rotate on a vertical axis drawn through its own center; the back part of the base is pressed inward toward the vestibule, while the forepart is withdrawn from it. By the action of the muscle the tension of the fluid within the internal ear is probably increased.
The Mucous Membrane of the Tympanic Cavity is continuous with that of the pharynx, through the auditory tube. It invests the auditory ossicles, and the muscles and nerves contained in the tympanic cavity; forms the medial layer of the tympanic membrane, and the lateral layer of the secondary tympanic membrane, and is reflected into the tympanic antrum and mastoid cells, which it lines throughout. It forms several vascular folds, which extend from the walls of the tympanic cavity of the ossicles; of these, one descends from the roof of the cavity to the head of the malleus and upper margin of the body of the incus, a second invests the Stapedius muscle: other folds invest the chorda tympani nerve and the Tensor tympani muscle. These folds separate off pouch-like cavities, and give the interior of the tympanum a somewhat honey-combed appearance. One of these pouches, the pouch of Prussak, is well-marked and lies between the neck of the malleus and the membrana flaccida. Two other recesses may be mentioned: they are formed by the mucous membrane which envelops the chorda tympani nerve and are situated, one in front of, and the other behind the manubrium of the malleus; they are named the anterior and posterior recesses of Troltsch. In the tympanic cavity this membrane is pale, thin, slightly vascular, and covered for the most part with columnar ciliated epithelium, but over the pyramidal eminence, ossicles, and tympanic membrane it possesses a flattened non-ciliated epithelium. In the tympanic antrum and mastoid cells its epithelium is also non-ciliated. In the osseous portion of the auditory tube the membrane is thin; but in the cartilaginous portion it is very thick, highly vascular, and provided with numerous mucous glands; the epithelium which lines the tube is columnar and ciliated.
Vessels and Nerves.The arteries are six in number. Two of them are larger than the others, viz., the tympanic branch of the internal maxillary, which supplies the tympanic membrane;