PART II. THE MIDDLE EAR. (Part 3)

pus. It is perforated by the glosso-pharyngeal nerve and a minute vessel. Studied with an eye to pathological conditions, some of these walls present very important relations. Thus the roof of the tympanum lies in contact with the meninges of the brain, so that in caries of this wall the patient may die of purulent meningitis or cerebritis. Again, caries of the lower wall may be followed by phlebitis of the jugular vein ; while caries of the inner wall has sometimes caused destruction of the coats of the carotid artery and fatal hemorrhage, also a suppurative inflammation of the labyrinth, with exten- sion into the cavity of the skull. It is easy to see, too, how even a non-suppurative inflammation of the tympanum may affect the facial nerve, since, during a part of its course, the nerve is separated from the mucous membrane by only a thin plate of bone, which may even be deficient in many places. Indeed, swelling of this nerve, causing temporal facial paraly- sis, or destruction of it, producing permanent paralysis, is not uncommon in connection with a suppuration in the middle ear. 200 OSSICULA AUDITUS. OSSICULA AUDITUS. 3. The three small bones of the ear, the ossicula avditvs, which serve for the conduction of the sonorous undulations through the tympanum to the labyrinth, are the malleus, or hammer ; the incus, or anvil ; and the stapes, or stirrup. The malleus may be described as consisting of the head, neck, short process, manubrium or handle, and the long pro- cess or processus gracilis.* The head is the larger, upper extremity of the bone. Posteriorly it has an elliptical de- pression, twice or thrice as long as it is broad, and of con- siderable depth for articulation with the incus. Below the head is a constricted portion called the neck, and just below this, and on the upper end of the manubrium, is a promi- nence to which the processes are attached. The manu- brium extends downward and inward, being inserted into the drum-membrane between the circular and radiating fibres of the middle layer. The processus gracilis passes from the eminence below the neck forward and outward to the Glaserian fissure. The short process lies at the base of the manubrium opposite where it gives attachment to the tensor tympani. The incus lies just back of the malleus, and may be de- scribed as having a body and two processes On the anterior and inner surface of the head is seen the surface for articula- tion with the malleus. The short process projects backward and articulates with the posterior wall of the tympanum. The long process, much more slender than the other, descends at a right angle with the short process, and parallel with and behind the manubrium, to end in the processus lenticularis which articulates with the head of the stapes. This articulation lies a little higher than the tip of the manubrium. The stapes consists of the head, neck, crura and base, and * Some writers call the handle of the malleus the long process. OSSICULA AUDITUS. 201 is the innermost and smallest of the bones of the ear, and indeed of the body. The head presents on its outer part a surface for articulation with the lenticular process of the long process of the incus. Just internally to the head is the con- stricted portion called the neck, into "which is inserted the stapedius muscle. From the neck the crura diverge horizon- tally, the one forward and inward, the other backward and The Ossicula Auditus of the Left, Cavity of the Tympanvm, seen from 1. The malleus, icith the handle running downwards, and the processus gracilis running to the running to the left, and its long process in right. 3. The incus, with its shm^t articulation with the stapes. 3. Th Tlie Ossicula Auditus of the Bight Cavity of the Tympanum, seen from within. 1. The head of the malleus. 2. The processus gracilis. 3. The long p?vcess, or handle. 4. Long process of the incus. 5. The short process of the incus. 6. The stapes. Tlie Bight Annulus Tympanicus, or Long Bing, of the Newly Born, seen from zoithout. 1. The anterior thicker part, in the newly born, lies next to the Glaserian fissure, which is quite toide, and just behind the condyloid fo?sa unites with the squamous portion of the temporal bone. 2. A process on the posterior half of the ring, about the middle, which is always present in varying degrees of development.— {From Budinger,s Photographic Atlas des Menschlic/ien Gehororganes.) inward, to be inserted into a thin plate constituting the base, which lies upon the membrane of the fenestra oval is. On the outer side of the base is a delicate ridge running from the extremities of the crura and into which is inserted the obtu- rator stapedis. 4. Of the ligaments of the ossicles we have two classes : the ligaments of the movable joints and those of the immovable joints. The malleo-incus joint may be classed with the gynglimus 202 OSSICULA. AUDITUS. articulations on account of the character of the articulating surfaces. These surfaces are covered by cartilage about 0.04mm. in thickness. The capsule is tense. This joint is provided with synovial membrane. The articulation between the short process of the incus and the posterior tympanic wall is an amphiarthrosis, and is surrounded by a tolerably thick and tense capsule. The mo- tion is quite restricted. The joint between the processus lenticularis of the incus and the head of the stapes is an arthrosis, the processus len- ticularis corresponding to the ball and the head of the stapes to the socket. Both surfaces are covered with cartilage. The cartilage is much more delicate than those of the other joints, and is characterized by being rich in elastic fibres. • The ligamentum obturatorium stapedis is a thin membrane inserted into the ridge on the outer side of the base of the stapes and into the inner edges of the crura, closing the open- ing formed by these parts. The head of the malleus lies sometimes in contact with the roof of the tympanic cavity. More frequently it is connected with the roof by the cylindrical lig. mallei sivperius {Soemmering). The neck of the malleus is held in place by the cartilage which sometimes takes the place of the long process, and by the lig. mallei anierius (Arnold), which goes from the spina angularis of the sphenoid parallel with the fissura petro-tympanica to be inserted upon the head of the malleus. The incus, when not in immediate contact with the roof of the tympanum, is attached to the roof by means of the lig. incudis swperius (Arnold), and is inserted into the posterior border of the body of the bone. 5. The tensor tympani muscle arises in front of the anterior opening of the canalis musculo-tubarius from the pyramid of the temporal bone, from the upper wall of the tubal cartilage and from the neighboring border of the sphenoid. It passes over the septum tubas into and through the canal of the tensor tympani. Just before leaving the canal it becomes tendinous. The tendon at the extremity of the canal turns outward and runs nearly at a right angle with the muscular part to the base of the manubrium mallei. BLOOD-VESSELS OF THE TYMPANUM. 203 The stapedius muscle arises from the bottom of the pyra- mid, or emineritia stapedii, the hollow of which it fills. At the orifice of the canal it becomes tendinous, and thence runs, at an obtuse angle with the rest of the muscle, to the neck of the stapes. This is the smallest distinct muscle of the human body. 6. The mucous membrane of the tympanum is a continuation of that of the Eustachian tube and naso-pharyngeal space. It is extremely delicate and consists chiefly of an epithelium and a layer of connective tissue underneath. On the lower, the anterior portion of the inner, and the posterior walls, the epithelium consists mainly of columnar cells ; while on the promontory, roof, membrana tympani and ossicles, pavement cells predominate. The thinness of the connective tissue is such that Von Troltsch asserts that the mucous membrane cannot be separated from the periosteum, and that every catarrh is a periostitis. But, according to Kessel, the connective tissue of the mucous membrane in some places forms a fibrous frame-work which separates from the periosteum, and passes from one projection of bone to another through the free space of the cavity. One such bridge has frequently been observed to pass from the eminentia pyramidalis to the processus cochleariformis, while many are seen on the floor of the tympanum. BLOOD-VESSELS. The tympanum receives its nutrition from five sources : 1. The tympanic branch of the internal maxillary which supplies the membrana tympani. 2. The stylo-mastoid branch of the posterior auricular which supplies the back part of the tympanum and mastoid cells. 3. The petrosal branch of the middle meningeal and branches of the ascending pharyngeal and internal carotid. The veins of the tympanum empty into the middle menin- geal and pharyngeal. NERVES. The tensor tympani muscle is supplied by a branch from 204 NERVES OP THE TYMPANUM. the otic ganglion, and from the internal pterygoid, a branch of the third division of the trifacial. The stapedius is supplied by a filament from the facial nerve. The nerves of the mucous membrane are derived from the tympanic plexus, consisting of a combination of the great sym- pathetic, the trifacial, and the glossopharyngeal. The nerves that make up the tympanic plexus, according to Yon Troltsch,* are 1. Several carotico-tympanic nerves, branches from the plexus of the sympathetic in the carotid canal, which enter the cavity of the tympanum through special foramina. 2. A twig of the superficial petrosal nerve, entering the cavity from above. It is regarded by some as a connection between the otic ganglion and bend of the facial. Others consider it a continuation of the tympanic nerve (Jacobson's) to the otic ganglion. 3. The ramifications of the tympanic nerve, arising from the glosso-pharyngeus. The otic ganglion is situated near the foramen ovale of the greater wing of the sphenoid bone, in front of the middle meningeal artery, on the outer side of the cartilage of the Eustachian tube, and the point of origin of the tensor palati muscle. It is made up of motor fibres from the third division of the fifth nerve, of sensory fibres from the glosso-pharyngeal, and of fibres from the great sympathetic. Its branches of distribution are to the tensor tympani and the tensor palate muscles. It sends a twig to the external pterygoid branch of the fifth nerve, and several communicating branches to the auricular nerve of the third branch of the fifth nerve. By this ganglion the soft palate, the drum -head and tensor tympani, and the integument of the external ear are put in relation with each other and with the general nervous system. —{Von Troltsch.) The chorda tympani nerve seems to pass through the tym- * Treatise on the Ear, American translation, p 97. MASTOID PROCESS. 205 panic cavity without being in any physiological relation to it. Division of this nerve in operations upon the tensor tympani muscle usually has no effect upon the functions of the ear.* THE MASTOID PROCESS. The mastoid portion of the temporal bone (fiaorog, a nipple or teat) is situated at the posterior part of the temporal bone. Its external surface is rough, and perforated by numerous foramina. One of these, of large size, situated at the poste- rior border of the bone, is called the mastoid foramen. Through it passes a vein to the transverse sinus and a small artery. This roughened appearance of the mastoid is sometimes so marked that it resembles the inner cellular structure of the bone. In some rare cases there is even complete absence of the outer layer of bone, so that the air cavities open exter- nally, as well as into the cavity of the tympanum and the external auditory canal. Gruber t has seen emphysema of the neck and of the occi- pital region result from the inflation of the cavity of the tym- panum in cases where such external openings existed under the skin. This foramen does not always exist in the mastoid process, but is sometimes found in the occipital bone, or in the suture between the temporal and the occipital. The mastoid portion is continued below into a conical pro- jection, which is the true mastoid process. To this process are attached the sterno-mastoid, the splenius capitis, and trachelo-mastoid muscles. On the inner side of the mastoid process is a deep groove, called the fossa sigmoidea (see cut on page 197). In this groove is a part of the lateral sinus, and the mastoid foramen opens into it. The mastoid process is hollowed out into a number of spaces of various size, which are called the mastoid cells. * See Chapter X. for an account of the functions of the chorda tympani. f Lehrbuch, p. 32. 206 THE MASTOID CELLS. THE MASTOID CELLS. The upper or horizontal part of the process, called also the antrum mastoideum, is in communication with the tympanum by means of one or more openings in the posterior tympanic wall ; and since it exists even in the infant, before the develop- ment of the mastoid process, it has been suggested that the name of "upper cavity of the tympanum" would be more appropriate. The second part of these cells, lying in the mas- toid process of the temporal bone, are below the horizontal part. The whole consist of a great number of irregular spaces of varying sizes — sizes that also vary much in different indivi- duals. The whole are enclosed by a dense cortical layer of bone, separating them from the cavity of the skull, and limit- ing them externally. This cortical layer also is of different thicknesses in different individuals, a fact of some practical importance in cases of suppurative inflammation of the mid- dle ear implicating these cells. Several small foramina are seen in the mastoid portion of the temporal bone — openings for branches of the middle meningeal artery and the vasa emissaria Santorini. The cells are lined by a mucous membrane similar to that of the membrana tympani, but it is more delicate. The epithelium consists of smooth cells of the same con- sistency and arrangement as those of the membrana tympani. Under this we find two layers of connective tissue, correspond- ing to the periosteum. The latter layer contains numerous nerves, and blood and lymph vessels. The upper layer very frequently separates itself at the free edge of the cells, like a membrane, and becomes attached to more closely lying tips or projections of bone. By this means the cavities of two cells lying next each other become separated. In the larger cells these membranes are stretched horizontally, like cur- tains, by means of processes which arise from them. — (Kessel.)* At birth the mastoid process is but the rudiment of what it is afterwards to be. It is a small tuberosity, and contains but * Handbuch der Lehre von den Geweben. Vierte Lieferung, p. 864 THE MASTOID CELLS. 207 one cell of any considerable size, which afterwards becomes the mastoid antrum. Dr. Giovanni Zoja* of Pavia, examined sixty-eight fresh preparations, and one hundred dry ones, in order to get the average size of the mastoid process and its cavities. The result of his investigations is, that the breadth of the mastoid is 19 millimetres, its thickness 13mm., and its length 12mm. About one millimetre should be deducted from these measure- ments in the bone of the female subject. Zoja does not con- firm Velpeau's view, that the mastoid process is more devel- oped in advanced life. The cortical layer, according to these examinations, has an average thickness of from one to two millimetres. In two of the sixty-eight specimens belonging to one subject the cells were united into one large cavity, so that they formed, as it were, a mastoid cavity. This was also found in another case on one side only. The cells in the centre of the process are usually the larger, and communicate with one another, if they are not separated by the membane that has been described. In several cases there were cells only in the base of the process. Occasionally these cells extended to the side of the skull, or even to the middle of the petrous part of the temporal bone. Dr. Zoja thinks that the development of the cellular struc- ture goes on in a kind of system. They become gradually larger, they are lined with a peculiar membrane, in the spaces a gelatinous mass is found, which becomes gradually serous, and is either taken up by the vessels of the cavities or passes into the cavity of the tympanum, where it is absorbed. In five of the sixty-eight specimens the antrum was found to be separated from the other cellular spaces by a membran- ous partition.? BLOOD-VESSELS OP THE MASTOID PROCESS. The blood supply of the mastoid cells is furnished by the stylo-mastoid branch of the posterior auricular artery, while their nerves come from the tympanic plexus. * Gruber's Lelirbuch, p. 33. t Henle, Lelirbuch, p. 751. 208 EUSTACHIAN TUBE. THE EUSTACHIAN TUBE. } The Eustachian tube, like the external auditory meatus, consists of an osseous and a cartilaginous part. The forinei Section of the I, showing the Divisions of the Ear and the Nasopharyngeal Cavity. After a Photograph— Budinger. Cartilage of external auditory canal. 2. panorvm. 5. Cavity of the tympanum seous auditory canal. 3, 4, Membranm Tym- 6. Dilator muscle of the Eustachian tube. 1. Levator palati muscle" 8. Mucous membrane of the pharyngeal orifice of the tube 9. Left membrana tympani. 10. Handle of the malleus and short process. 11. Tensor tym- pani muscle. 12. Mucous membrane of the membranous portion of the