164 THE ANATOMY OF THE HORSE. 



"soon as the ear is finished. On one side the muscles and cartilages of 

 the ear may be dissected ; and then the other side may be denuded 

 of skin in the same manner as the first, in order to follow the vessels 

 and nerves. 



Muscles of the Ear. — These are divided into extrinsic and intrinsic. 

 The former have their origin from extraneous parts, but the latter 

 both arise from, and are inserted into, the cartilages of the ear. The 

 cartilages of the ear cannot be fully exposed until the muscles have 

 been examined, but it may be premised that the conchal cartilage 

 is the large trumpet-like cartilage which mainly gives to the outer 

 ear its form ; that the annular cartilage is a short tube, or ring, 

 which is telescoped on to the external auditory process, and is itself 

 embraced by the constricted base of the concha ; and that the scuti- 

 form cartilage is a thin plate which rides on the surface of the temporal 

 muscle, in front of the base of the concha. 



Extrinsic Muscles : — 



The Parotido-auricularis, or Deprimens Aurem (Plate 29). This 

 muscle has the form of a broad riband. It arises from the outer surface 

 of the parotid gland ; and, passing vertically upwards, it is inserted 

 into the outer part of the base of the concha, below the opening. 



Action. — To incline the ear downwards and outwards. 



The Cervico - auriculares, or Retrahentes Aurem. There are 

 three of these, distinguished as the cervico-auricularis (or retrahens) 

 externus, medius, and internus. They all arise from the poll in the 

 neighbourhood of the insertion of the ligamentum nuchse, and they 

 are here superposed the one to the other. Suppose the ear to be 

 placed with the opening of the concha looking directly outwards, 

 then the externus is inserted into the middle of the inner face of the 

 concha; the medius into the outer side of the concha, beneath the 

 opening, and under cover of the parotido-auricularis muscle ; and 

 the internus into the base of the concha, on its posterior aspect, 

 and under cover of the parotid gland. 



Action. — In moderate contraction these muscles give the opening of 

 the concha an outward direction ; and when forcibly contracted they 

 direct the opening backwards as well as outwards, and incline the ear 

 towards the poll. 



The Parieto-auricularis Externus, or Attolens Maximus. This is 

 a wide, membranous muscle covering the temporalis muscle. It arises 

 from the parietal crest; and it is inserted by its upper fibres into the 

 scutiform cartilage, and by its lower into the front of the conchal 

 cartilage. Its upper fibres are, at their origin, continuous across the 

 middle line with the opposite muscle. 



Action. — To prick the ear, that is, to erect it and give its opening a 

 forward direction. 



