ANATOMY OF EXTERNAL EAR - Dr.G.Bhanu Prakash

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The outer ear is situated superficially next to several bony landmarks. It is posterior to the zygomatic process of the temporal bone as well as the proximal part of the mandibular process and the auricular surface of the mandibular notch. Superior to it is the squamous part of the temporal bone, while the styloid process is located inferiorly. Finally, the mastoid process of the temporal bone lies posteroinferiorly with respect to the outer ear. There is very little subcutaneous tissue between the auricular scaffold and the overlying skin of the ear. The skin, however, continues into the external acoustic meatus and covers the lateral surface of the tympanic membrane.

Before the different parts of the external ear can be discussed, it is important to note that the left and right ears are optical isomers of themselves (similar to the left and right hands). This is relevant because the different parts of the external ear can be related to a clock face. However, the position of one structure, for example the tragus, will be in a 9 o’clock position on the left, but in a 3 o’clock position on the right. The left ear will be used as an example throughout, but keep in mind the mirroring necessary to discuss the right ear.

On that note, the tragus is the first of several cartilaginous flaps in the ear. As previously mentioned, it projects posteriorly from the 9 o’clock position to provide a lateral border to the distal end of the external acoustic meatus. Posteroinferior to the tragus in the 5 o’clock position is the antitragus. It is also a cartilaginous structure that is separated from the tragus by an intertragic notch. Superior to the tragus in the 10 o’clock position is the crus of the helix. It starts at the concha of the auricle (depression at the orifice of the external auditory meatus that corresponds with the protruding eminentia conchae on the posterior surface of the ear) and extends anterosuperiorly in the 10 o’clock position (superior to the tragus) and continues as the prominent ridge known as the helix. The helix is the outermost concaved section of the ear and it has a small protuberance at the 2 o’clock position called the auricular tubercle. The helix continues inferiorly and ends in the 4 o’clock position at the tail of the helix. Another raised cartilaginous structure called the antihelix mirrors the path of the helix. Apically, the antihelix has two crura surrounding a depression known as the triangular fossa. The antihelix is separated from the helix by the scaphoid fossa (corresponding to the eminentia scaphae on the posterior aspect of the external ear). Finally, in the 6 o’clock position is the soft, fibrofatty structure called the lobule.

There are two groups of muscles associated with the external ear. The intrinsic group of muscles consists of the tragicus and antitragicus, obliquus auriculae, transversus auriculae and the helicis major and minor. The tragicus muscle lies vertically on the lateral aspect of the tragus. It is a flat, short muscle that is perpendicular to (but not in contact with) the antitragicus muscle. Antitragicus originates from the anteroinferior part of the antitragus to the tail of the antihelix and helix. Helicis minor travels obliquely along the crus of the helix, while helicis major courses over the anterior boundary of the helix after travelling vertically over its spine. The obliquus auriculae and transversus auriculae muscles are found on the posterior (cranial) part of the external ear. The former extends from the upper part of the eminentia scaphae to the eminentia conchae, while the latter bridges the inferior aspect of the same two structures.

The extrinsic muscle group includes the anterior, posterior and superior auricular muscles. Auricularis posterior originates as three aponeurotic muscular fasciculi from the mastoid process to insert in the ponticulus (oblique ridge on the eminentia conchae) on the cranial aspect of the external ear. Auricularis anterior begins in the epicranial aponeurosis and inserts in the spine of the helix. It is the smallest of the three extrinsic muscles. Thirdly, auricularis superior is the largest of the extrinsic muscles. It also begins at the epicranial aponeurosis and inserts in the cranial part of the auricle.

The extrinsic muscles have limited impact on the movement of the external ear. The intrinsic muscles, however, are able to modify the shape of the auricle to a minor degree. Helicis major is known to move the auricle anteriorly and superiorly.

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