Part 224

The =auricular muscles= may be subdivided into two sets, viz., (a) extrinsic muscles, which arise on the head and adjacent part of the neck, and move the external ear as a whole, and (b) intrinsic muscles, which are confined to the auricula. In this connection the scutiform cartilage may be regarded as a sesamoid cartilage intercalated in the course of some of the muscles.

The =extrinsic muscles= are as follows:

1. The =scutularis= is a thin muscular sheet situated subcutaneously over the temporalis muscle. Its fibers arise from the zygomatic arch and the frontal and sagittal crests, and converge to the scutiform cartilage. It consists of three parts.

(a) The =fronto-scutularis= comprises temporal and frontal parts, which arise from the zygomatic arch and the frontal crest, and are inserted into the outer and anterior borders of the scutiform cartilage respectively.

(b) The =interscutularis= arises from the sagittal crest, over which it is in part continuous with the muscle of the opposite side. Its fibers converge to the inner border of the scutiform cartilage.

(c) The =cervico-scutularis= is not well defined from the preceding muscle. It arises from the occipital crest and is inserted into the inner border of the scutiform cartilage.

2. The =anterior auricular muscles= (Mm. auriculares nasales) are four in number.

(a) The =zygomatico-auricularis= arises from the zygomatic arch and the parotid fascia, and is inserted into the outer face of the base of the conchal cartilage under cover of the parotido-auricularis.

(b) The =scutulo-auricularis superficialis inferior= arises on the outer part of the superficial face of the scutiform cartilage and ends on the base of the conchal cartilage with the preceding muscle.

(c) The =scutulo-auricularis superficialis medius= arises from the posterior part of the deep surface of the scutiform cartilage and is inserted into the dorsum of the conchal cartilage, close to the lower part of its anterior border and above and behind the preceding muscle. It receives a slip from the cervico-scutularis.

(d) The =scutulo-auricularis superficialis superior= is a thin slip which is detached from the interscutularis over the inner border of the scutiform cartilage. It ends on the anterior aspect of the lower part of the dorsum of the conchal cartilage.

3. The =superior auricular muscles= (Mm. auriculares dorsales) are two in number.

(a) The =scutulo-auricularis superficialis accessorius= is a narrow band which is largely covered by the preceding muscle. It arises from the posterior prolongation and the adjacent part of the superficial face of the scutiform cartilage, and is inserted into the convex surface of the conchal cartilage internal to the preceding muscle, the two crossing each other at an acute angle.

(b) The =parieto-auricularis= is flat and triangular; it arises from the sagittal crest under cover of the cervico-scutularis, runs outward and a little backward, and is inserted by a flat tendon into the lower part of the convex surface of the concha under cover of the cervico-auricularis superficialis.

4. The =posterior auricular muscles= (Mm. auriculares caudales) are three in number.

FIG. 563.—EXTERNAL EAR OF HORSE AND ITS MUSCLES, LATERAL VIEW.

2, Posterior border; 3, anterior border of auricula; 8, scutiform cartilage; 9, zygomatic arch; n, parotido-auricularis; o, zygomatico-auricularis; o′, scutulo-auricularis superficialis inferior; o″, scutulo-auricularis superficialis medius et superior; p, interscutularis; p′, fronto-scutularis (pars temporalis); q, cervico-auricularis profundus major; s, small (or anterior) oblique muscle of head; t, splenius; y, tendon of mastoido-humeralis; c, mastoido-humeralis; x, wing of atlas. (After Ellenberger-Baum, Anat. für Künstler.) ]

(a) The =cervico-auricularis superficialis= is a thin triangular sheet. It is wide at its origin from the occipital crest and the adjacent part of the ligamentum nuchæ, and becomes narrower as it passes outward to be inserted into the inner side of the convex surface of the concha.

(b) The =cervico-auricularis profundus major= arises from the ligamentum nuchæ, partly beneath and partly behind the preceding muscle. It is directed outward and is inserted into the postero-external aspect of the base of the ear, partly under cover of the parotido-auricularis.

(c) The =cervico-auricularis profundus minor= arises under the preceding muscle and passes downward and outward to be inserted into the lowest part of the convex surface of the concha, partly under cover of the parotid gland.

5. The =parotido-auricularis= (s. M. auricularis inferior) is a ribbon-like muscle which lies on the parotid gland. It is thin and wide at its origin from the fascia on the lower part of the parotid gland and becomes somewhat narrower and thicker as it passes upward. It is inserted into the conchal cartilage just below the angle of junction of its borders.

6. The =deep auricular= or =rotator muscles= (M. auriculares profundis, rotatores auriculæ), two in number, are situated under the scutiform cartilage and the base of the concha and cross each other.

(a) The =scutulo-auricularis profundus major= is the strongest of the auricular muscles. It is flat and is about an inch wide. It arises from the deep face of the scutiform cartilage and passes backward to end on and below the most prominent part of the base of the concha (eminentia conchæ).

(b) The =scutulo-auricularis profundus minor= lies between the base of the concha and the preceding muscle, and is best seen when the latter is cut and reflected. It is flat and about an inch in length. It arises from the posterior part of the deep face of the scutiform cartilage and from the cervico-scutularis, and passes downward, backward, and outward to be inserted into the base of the concha under cover of the preceding muscle.

FIG. 564.—MUSCLES OF EXTERNAL EAR OF HORSE, VIEWED FROM ABOVE.

On the right side parts of the superficial muscles have been removed and the scutiform cartilage turned back to display the deeper muscles. a, Frontal part, a′, temporal part of fronto-scutularis; b, interscutularis; c, cervico-scutularis; d, e, scutulo-auricularis superficialis superior and medius; f, zygomatico-auricularis; g, scutulo-auricularis superficialis accessorius; o, cervico-auricularis superficialis; q, scutulo-auricularis superficialis inferior; t, scutiform cartilage; u, parieto-auricularis; v, cervico-auricularis profundus major; w, cervico-auricularis prof. minor; x, x′, scutulo-auricularis prof. major et minor; y, temporalis. (Ellenberger-Baum, Anat. d. Haustiere.) ]

7. The =tragicus= or mastoido-auricularis is a small muscle which arises from the temporal bone just behind the external auditory process and from the annular cartilage; it passes upward to be inserted into the lower part of the anterior border of the conchal cartilage.

The =intrinsic muscles= are very small and of little importance. They are as follows: