Chapter 56
XIV. The External Ear. The external ear consists of the expanded portion named the auricula or pinna and the external acoustic meatus. The former projects from the side of the head and serves to collect the vibrations of the ear by which sound is produced.
The latter leads inward from the bottom of the auricula and conducts the vibrations to the tympanic cavity. The auricula or pinna is of an ovoid form, with its larger end directed upward. Its lateral surface is irregularly concave, directed slightly forward and presents numerous eminences and depressions to which names have been assigned.
The prominent rim of the auricula is called the helix. Where the helix turned downward behind a small tubercle, the auricular tubercle of Darwin is frequently seen. This tubercle is very evident about the sixth month of fetal life when the whole auricula has a close resemblance to that of some of the adult monkeys.
Another curved prominence parallel with and in front of the helix is called the antihelix. This divides above into two crura between which is a triangular depression, the fossa triangularis. The narrow curved depression between the helix and the antihelix is called the scapha. The antihelix describes a curve around a deep capacious cavity, the concha, which is
partially divided into two parts by the cruse or commencement of the helix. The upper part is termed the simpa conchi, the lower part the cavum conchi. In front of the concha and projecting backward over the meatus is a small pointed eminence, so called from its being generally covered on its undersurface with a tuft of hair resembling a goat's beard.
Opposite the tragus and separated from it by the intertragic notch is a small tubercle, the antitragus. Below this is the lobule composed of tough, arylia and adipose tissues and wanting the firmness and elasticity of the rest of the auricula. The cranial surface of the auricula presents elevations which correspond to the depressions
on its lateral surface and after which they are named. Example, eminentia conchi, eminentia triangularis, etc. Structure The auricula is composed of a thin plate of yellow fibrocartilage covered with intigument and connected to the surrounding parts by ligaments and muscles and to the commencement of the external acoustic meatus by fibrous
tissue. The skin is thin, closely adherent to the cartilage and covered with fine hairs furnished with sebaceous glands which are most numerous in the concha and scaphoid fossa. On the tragus and antitragus the hairs are strong and numerous. The skin of the auricula is continuous with that lining the external acoustic meatus.
The cartilage of the auricula, cartilago auriculae, cartilage of the pinna, consists of a single piece. It gives form to this part of the ear and upon its surface are found the eminences and depressions above described. It is absent from the lobule.
It is deficient also between the tragus and beginning of the helix, the gap being filled up by dense fibrous tissue. At the front part of the auricula where the helix bends upward is a small projection of cartilage called the spinahelicus. While in the lower part of the helix the cartilage is prolonged downward as a tail-like process,
the caudahelicus. This is separated from the antihelix by a fissure, the fissura antitragohelicona. The cranial aspect of the cartilage exhibits a transverse furrow, the sulcus antihelicus transversus, which corresponds with the inferior crues of the antihelix and separates the eminentia concha from the eminentia triangularis.
The eminentia concha is crossed by a vertical ridge, ponticulus, which gives attachment to the auricularis posterior muscle. In the cartilage of the auricula are two fissures, one behind the crues helicus and another in the tragus. The ligaments of the auricula, ligamenti auricularia, valsalva, ligaments of the pinna, consist
of two sets. One, extrinsic, connecting it to the side of the head. Two, intrinsic, connecting various parts of its cartilage together. The extrinsic ligaments are two in number, anterior and posterior. The anterior ligament extends from the tragus and spinohelicus to the root of the zygomatic
process of the temporal bone. The posterior ligament passes from the posterior surface of the concha to the outer surface of the mastoid process. The chief intrinsic ligaments are a, a strong fibrous band stretching from the tragus to the commencement of the helix, completing the meatus in front and partly encircling
the boundary of the concha, and b, a band between the antihelix and the caudahelicus. Other less important bands are found on the cranial surface of the pinna. The muscles of the auricula consist of two sets. One, the extrinsic, which connect it with the skull and scalp and move the auricula as a whole, and two, the intrinsic, which extend from one part of the auricle to another.
The extrinsic muscles are the auricularis anterior, superior, and posterior. The auricularis anterior, atrahens aurum, the smallest of the three, is thin, fan-shaped, and its fibers are pale and indistinct. It arises from the lateral edge of the gallia, aponeurotica, and its fibers converge to be inserted into a projection on the front of the helix.
The auricularis superior, atrahens aurum, the largest of the three, is thin and fan-shaped. Its fibers arise from the gallia aponeurotica and converge to be inserted by a thin, flattened into the upper part of the cranial surface of the auricula. The auricularis posterior, atrahens aurum, consists of two or three fleshy fasciculi, which arise from the mastoid portion of the temporal bone by short aponeurotic fibers.
They are inserted into the lower part of the cranial surface of the concha. Actions. In man, these muscles possess very little action. The auricularis anterior draws the auricula forward and upward. The auricularis superior slightly raises it, and the auricularis posterior draws it backward.
The intrinsic muscles are the helicous major, helicous minor, tragegus, antotragegus, transversus auriculi, obliquus auriculi. The helicous major is a narrow, vertical band situated upon the anterior margin of the helix. It arises below from the spina helicus and is inserted into the anterior border of the helix, just where it is about to curve backward.
The helicous minor is an oblique fasciculus covering the cruce helicus. The tragegus is a short, flattened, vertical band on the lateral surface of the trageus. The antotragegus arises from the outer part of the antotrageus and is inserted into the caudahelicus and antihelix. The transversus auriculi is placed on the cranial surface of the pinna.
It consists of scattered fibers, partly tendinous and partly muscular, extending from the eminentia concha to the prominence corresponding with the scapha. The obliquus auriculi, also on the cranial surface, consists of a few fibers extending from the upper and back part of the concha to the convexity immediately above it. Nerves
The auricularis anterior and superior and the intrinsic muscles on the lateral surface are supplied by the temporal branch of the facial nerve. The auricularis posterior and the intrinsic muscles on the cranial surface by the posterior auricular branch of the same nerve. The arteries of the auricula are the posterior auricular from the external carotid, the anterior
auricular from the superficial temporal, and a branch from the occipital artery. The veins accompany the corresponding arteries. The sensory nerves are the great auricular from the cervical plexus, the auricular branch of the vagus, the auriculotemporal branch of the mandibular nerve, and the lesser occipital from the cervical plexus.
The external acoustic meatus, meatus acousticus externus, external auditory canal or meatus, extends from the bottom of the concha to the tympanic membrane. It is about 4 centimeters in length if measured from the tragus. From the bottom of the concha, its length is about 2.5 centimeters. It forms an S-shaped curve and is directed at first inward, forward, and slightly upward,
pars externa. It then passes inward and backward, pars media, and lastly is carried inward, forward, and slightly downward, pars interna. It is an oval cylindrical canal, the greatest diameter being directed downward and backward at the external orifice, but nearly horizontally at the inner end.
It presents two constrictions, one near the inner end of the cartilaginous portion and another, the ithsmus, in the osseous portion, about 2 centimeters from the bottom of the concha. The tympanic membrane, which closes the inner end of the meatus, is obliquely directed. In consequence of this, the floor and anterior wall of the meatus are longer than the roof
and posterior wall. The external acoustic meatus is formed partly by cartilage and membrane and partly by bone, and is lined by skin. The cartilaginous portion, meatus, acousticus, externus, cartilaginus, is about 8 millimeters in length.
It is continuous with the cartilage of the auricula and firmly attached to the circumference of the auditory process of the temporal bone. The cartilage is deficient at the upper and back part of the meatus, its place being supplied by fibrous membrane. Two or three deep fissures are present in the anterior part of the cartilage.
The osseous portion, meatus, acousticus, externus, osseous, is about 16 millimeters in length and is narrower than the cartilaginous portion. It is directed inward and a little forward, forming in its course a slight curve, the convexity of which is upward and backward. Its inner end is smaller than the outer and sloped, the anterior wall projecting beyond
the posterior for about 4 millimeters. It is marked except at its upper part by a narrow groove, the tympanic sulcus, in which the circumference of the tympanic membrane is attached. Its outer end is dilated and rough in the greater part of its circumference for the attachment of the cartilage of the auricula.
The front and lower parts of the osseous portion are formed by a curved plate of bone, the tympanic part of the temporal, which in the fetus exists as a separate ring, annulus tympanicus, incomplete at its upper part. The skin lining the meatus is very thin, adheres closely to the cartilaginous and osseous portions of the tube, and covers the outer surface of the tympanic membrane.
After maceration, the thin pouch of epidermis, when withdrawn, preserves the form of the meatus. In the thick subcutaneous tissue of the cartilaginous part of the meatus are numerous ceruminous glands, which secrete the earwax. Their structure resembles that of the suteriferous glands.
Relations of the meatus. In front of the osseous part is the condyle of the mandible, which, however, is frequently separated from the cartilaginous part by a portion of the parotid gland. The movements of the jaw influence to some extent the lumen of this latter portion. Behind the osseous part are the mastoid air cells, separated from the meatus by a thin
layer of bone. The arteries supplying the meatus are branches from the posterior auricular, internal maxillary, and temporal. The nerves are chiefly derived from the auriculotemporal branch of the mandibular nerve and the auricular branch of the vagus.
