872 THE SENSE ORGANS AND SKIN OF THE HORSE 



herent to the cartilage and is relatively dark in color. There are three or four 

 cutaneous ridges which run about parallel with the borders of the conchal cartilage, 

 but do not extend to the apex or the cavum conchas. The upper and marginal 

 parts and the ridges are covered with long hairs, but the skin between the ridges 

 and below is thin, covered sparsely with very fine hairs, and supplied with numerous 

 sebaceous glands. In the external acoustic meatus the skin becomes thinner; in 

 the cartilaginous part it is supplied with numerous large, coiled, ceruminous glands 

 (Glandulae ceruminosse) , and is sparsely covered with very fine hairs; in the osseous 

 part the glands are small and few or absent and there are no hairs. 



THE AURICULAR MUSCLES 



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 ex- 

 ternal ear as a whole, and (5) 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 

 parietal 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 lateral and 

 anterior borders of the scutiform cartilage respectively. 



(b) The interscutularis arises from the parietal crest, over which it is in part 

 continuous with the muscle of the opposite side. Its fibers converge to the medial 

 border of the scutiform cartilage. 



(c) The cervico-scutularis is not well defined from the preceding muscle. It 

 arises from the nuchal crest and is inserted into the medial border of the scutiform 

 cartilage. 



2. The anterior auricular muscles (Mm. auriculares orales) 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 partly 

 under, partly above, the insertion of the parotido-auricularis. 



(6) The scutulo-auricularis superficialis inferior arises on the lateral part of 

 the superficial face of the scutiform cartilage and ends on the base of the conchal 

 cartilage mth 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 de- 

 tached from the interscutularis over the medial border of the scutiform cartilage. 

 It ends on the anterior aspect of the lower part of the dorsum of the conchal car- 

 tilage. 



3. The dorsal 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 medial 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 parietal 

 crest under cover of the cervico-scutularis, runs outward and a little backward, 



