752 THE SENSE ORGANS AND SKIN OF THE HORSE 



cartilage behind the junction of its two borders, and are partially blended with the 

 insertion of the parotido-auricularis. 



2. The helicis is a small muscle attached in a position opposite to the preceding 

 on the anterior border of the conchal cartilage; it extends also into the depression 

 between the two divisions of the border. It is in part continuous with the insertion 

 of the parotido-auricularis. 



3. The verticalis auriculae^ is a thin stratum of muscular and tendinous fillers 

 which extends upward on the posterior surface of the concha from the eminentia 

 conchw. 



Actions. — The base of the concha is rounded and rests in a pad of fat (Corpus 

 adiposum auriculse), so that the movements of the external ear resemble those of 

 a ball-and-socket joint. It is noticeable that movements about the longitudinal 

 and transverse axes are accompanied by rotation. When the ear is vertical or 

 drawn forward ("pricked up"), the opening is usually directed forward; conversely, 

 when the ears are "laid back," the opening faces ])ackward. These movements 

 evidently result from the coordinated actions of several muscles which are very 

 complex and cannot be discussed in detail here. The scutularis acting as a whole 

 fixes the scutiform cartilage, so that the muscles which arise on the latter act 

 efficiently on the concha. The anterior auricular muscles in general erect the ear 

 and turn the opening forward. The interscutularis concurs in this action, causing 

 adduction and a symmetrical position of the ears; it also acts directly on the 

 conchal cartilage, since the scutulo-auricularis superficialis superior is in reality a 

 conchal insertion of the interscutularis. The scutulo-auricularis superficialis 

 accessorius draws the concha forward and turns the opening outward. The parieto- 

 auricularis adducts the concha and inclines it forward. The cervico-auricularis 

 superficialis is chiefly an adductor of the conchal cartilage, and directs the opening 

 outward. The cervico-auricularis jjrofundus major turns the opening outward and, 

 acting with the parotido-auricularis, inclines the ear toward the ])oll. The cervico- 

 auricularis profundus minor tends to direct the opening downward and outward. 

 The parotido-auricularis draws the ear downward and backward, and acts with the 

 cervico-auricularis profundus major in "laying back the ears"; the deep auricular 

 muscles concur in these actions. The tragicus shortens the external auditory canal. 

 The actions of the intrinsic muscles are inappreciable. 



The arteries of the external ear are derived from the anterior auricular branch 

 of the superficial temporal, the posterior or great auricular branch of the internal 

 maxillary, and the anterior branch of the occipital artery. 



The motor nerves to the muscles come from the auricular and auriculo-palpe- 

 bral branches of the facial nerve and from the first and second cervical nerves. 

 The sensory nerves are supplied by the superficial tem]X)ral branch of the mandibu- 

 lar nerve and the auricular branch of the vagus. 



THE MIDDLE EAR 



The middle ear (Auris media) or tympanic cavity (Cavum tympani) is a space 

 in the tympanic and petrous parts of the temporal bone situated between the mem- 

 brana tympani and the internal ear. It is a pneumatic cavity, which is lined by 

 mucous membrane, and communicates with the pharynx and the guttural i^ouch 

 by the Eustachian tube. It contains a chain of auditory ossicles by which the 

 vibrations of the membrana tympani are transmitted to the internal ear. 



The cavity consists of: (1) A main part or atrium, which lies immediately to 

 the inner side of the mem];)rana tympani; (2) the recessus epitympanicus, situated 

 a])ove the level of the membrane and containing the u])])er part of the malleus 



' Ellpnherger and Baum regard this as the homologue of the tz-ansversus and obHquus 

 auricula) of man. 



