Deep Cervico-auricular (Cervico-auricularis inferioris).—Covered by the preceding muscle and the superior portion of the parotid, it is inserted into the base of the pinna of the ear, and has the same action as the middle cervico-auricular.
Parotido-auricularis ([Fig. 92], 15).—This is a long and thin fleshy band which arises from the external surface of the parotid gland, and tapering as it passes upwards towards the pinna of the ear, is inserted into the external surface of the base of the concha, below the inferior part of the angle of reunion of the two borders which limit its opening.
It inclines the pinna outwards; it is, accordingly, an abductor of the pinna.
Temporo-auricularis Internus.—This muscle is covered by the external temporo-auricular and the superior cervico-auricular. It arises from the parietal crest, and is inserted into the internal surface of the concha. It is an adductor of the pinna of the ear.
There are, finally, an internal scuto-auricular muscle and a tympano-auricular; but they do not present any interest for us; we can simply confine ourselves to making mention of them.
In the ox, because of the situation of the temporal fossa and the fact that the external temporo-auricular muscle is applied, as in the horse, over the muscle which this fossa contains, this temporo-auricular muscle does not reach the middle line ([Fig. 91], 12).
But in the cat and the dog this muscle covers all the upper part of the head ([Fig. 90], 12). It is divided into two parts: the interscutellar and the fronto-scutellar.
The interscutellar is a single muscle, thin and broad, covering the temporal muscle and a portion of the occipital, extending from the scutiform cartilage of the pinna of one side to the same cartilage of the pinna belonging to the side opposite. It approximates the two pinnæ to one another by bringing them each into the position of adduction.
The fronto-scutellar arises from the orbital process of the frontal bone, and from the orbital ligament, which at this level completes the interrupted osseous boundary of the orbital cavity. Thence it is directed, widening as it proceeds, towards the scutiform cartilage, and is there inserted by blending with the corresponding part of the great zygomatic. Its action is analogous to that of the preceding muscle; but, further, it directs the opening of the pinna forwards.
These are the muscles which act, for example, when the dog, having his attention strongly attracted by any cause, pricks up his ears and turns the openings forward, in order the better to understand every sound which proceeds, or may possibly proceed, from that which he observes. From this, which may be extremely well seen in some individuals, results the appearance of vertical wrinkles of the skin in the interval between the pinnæ of the ears, these being caused by the folding of the integument, whilst the pinnæ approach one another. These movements, with which are associated fixation of look and a widening of the palpebral fissure, produce a peculiarly expressive look; this is why they merit our attention.