166 THE ANATOMY OF THE HORSE. 



The Parieto-auricularis Internus, or Attolens Posticus. This 

 muscle is to be exposed by the removal of the parieto-auricularis 

 externus, beneath the upper part of which it lies. It arises from 

 the upper part of the parietal crest ; and it is inserted into the 

 inner side of the concha, beneath the cervico-auricularis externus. 



Action, — It is the opponent of the parotido-auricularis, bringing the 

 ear into the erect position. 



The Mastoido-auricularis. This muscle is to be exposed by cutting 

 the preceding and the cervi co-auricular muscles, and forcibly depressing 

 the ear outwards. This will expose at the base of the ear a consider- 

 able quantity of fat, which is constantly present and facilitates the 

 movements of the ear. On clearing away this fat, the muscle will be 

 found at the inner side of the base of the ear. It forms a slender 

 fasciculus arising from the auditory process, and inserted into the base 

 of the concha. 



Action. — To telescope the conchal on the annular cartilage. 



Intrinsic Muscles : — 



Besides some scattered fibres on the outer and inner surfaces of the 

 concha, this group includes the following two distinct muscles passing 

 between the conchal and scutiform cartilages. 



The Scuto-auricularis Externus consists of two bundles of fibres 

 passing between the outer surface of the scutiform cartilage and the 

 inner side of the concha. 



Action. — To assist the parieto-auricularis externus in pricking the ear. 



The Scuto-auricularis Internus. In order to expose this muscle, 

 the scutiform cartilage is to be raised from the surface of the temporal 

 muscle, and turned upwards and outwards. The muscle is stronger 

 than the preceding, and consists of two distinct crossed bundles, which 

 arise from the inner surface of the scutiform cartilage, and pass 

 round the inner side of the base of the concha to get inserted into its 

 posterior aspect, above and internal to the insertion of the retrahens 

 internus. 



Action. — It opposes the preceding muscle, and assists the retrahentes 

 in rotating the concha so as to turn the opening outwards and back- 

 wards. 



Vessels : — 



The ear is supplied with blood by the anterior and posterior auricular 

 arteries. 



The Anterior Auricular Artery (Plate 28) is one of the two ter- 

 minal branches of the superficial temporal artery, which vessel divides 

 under the parotid gland, about an inch below the condyle of the lower 

 jaw. It ascends behind the capsular ligament of the jaw ; and, after 

 detaching muscular and cutaneous branches in front of the ear, it 

 enters the temporalis muscle. 



