This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The external auditory meatus, the tympanum, and the Eustachian tube are the remains of the first branchial cleft in the foetus. A failure of any portion of the cleft to close normally may leave small sinuses or depressions in the neighborhood of the ear. The external ear, also called the auricle or pinna, is composed mainly of a cartilaginous framework covered with thin skin; the lobe or lobule forms its lower part and is composed of dense connective tissue containing fat. The large concavity leading into the meatus is the concha. The skin of the ear is thin and moderately firmly attached to the cartilage. The subcutaneous tissue contains little or no fat. Although well supplied with blood, the exposed condition of the blood-vessels renders the ear sensitive to cold, and frost-bites are common. Injuries and wounds of the cartilage are slow to heal, and if inflamed the cartilage becomes exceedingly sensitive. Swelling of the ear readily occurs from injury or erysipelas, and the tension is quite painful.
Fig. 99. - The external ear.
Haematoma auris, or effusions of blood, occur from traumatism, especially in the insane. While a haematoma may occur between the skin and perichondrium, on account of the firm binding of the skin to the cartilage it is usually between the perichondrium and cartilage.
Angioma, or enlargement of the blood-vessels, not infrequently affects the external ear and may not only be disfiguring but, by showing a tendency to extension, may demand operation. The external ear derives its blood supply from the auricular branches of the temporal, internal maxillary, posterior auricular, and occipital arteries. As these are all branches of the external carotid, that artery is sometimes tied as a preliminary step to excising the angiomatous vessels.
Fig. 100. - Vertical section of the right ear.
The external auditory meatus extends from the concha to the drumhead, and is about 2.5 cm. in length. A little less than one-half of it is cartilaginous and a little over one-half bony. Viewed anteroposteriorly the canal has a slight curve with its convexity upward (Fig. 100). Viewed from above (Fig. 101), it is seen first to pass backward and then forward, forming an angle before the bony wall is reached. In order to look into the ear and see the membrane it is necessary to straighten the canal, either by inserting a speculum or by pulling the auricle outward, upward, and backward. In children, upward traction is not so necessary as in the adult. The length of the canal is approximately the same in childhood as in adults, but the bony part is still in a cartilaginous condition. The external opening is oval, while farther in the canal is more circular; hence the Gruber speculum, which is oval in shape, or the round speculum of Wilde can be used with almost equal satisfaction. The point of junction of the bony and cartilaginous parts is narrower than either end, and it is difficult to remove a foreign body which has passed this point. This is particularly true in children, the lumen of the external meatus being quite small and narrow while the tympanic membrane is nearly as large as in adults.
The floor is longer than the roof, owing to the drum membrane inclining at an angle of 140 degrees. Cartilage forms the lower part of the canal, while the upper
Fig. 101. - Right ear; horizontal transverse section part is completed by a fibrous membrane. Below and in front is the temporomaxillary joint, and just posterior is the glenoid lobe of the parotid gland. When the gland is inflamed and swollen it presses on the cartilaginous canal and produces pain; and in cases of suppuration pus may discharge through the external meatus, gaining access to the canal through fissures in the cartilage called the fissures of Santorini. The cartilaginous portion of the meatus contains sweat-glands, sebaceous glands, and hair-follicles. There are only a few glands in the upper posterior portion of the bony meatus. On account of the location of the glands in the external portion of the canal, accumulations of wax, and abscesses, which result from infection of the glands, occur nearer to the surface than to the drum membrane. It is only when the canal begins to fill up that the wax pushes its way to the membrane. When furuncles occur, the lining membrane swells and by closing the canal prevents a view of the drum being obtained. Incising of furuncles of the auditory meatus is sometimes required. The site of the inflamed spot having been located, an incision can be made where indicated. If care is exercised, one is not likely to injure the drum membrane, because the abscess starts in one of the sebaceous glands, which are located in the external half of the meatus. The membrane lies 2.5 cm. from the surface, and the point of the knife should not be carried so deeply as that for fear of wounding it; there is no necessity of going so far inward.
The meatus is supplied by the auriculotemporal branch of the fifth and the auricular branch of the pneumogastric nerve. Irritation of the latter nerve is said to be the cause of feeling it in the throat when anything is put in the ear.