Occipito-Frontalis.—The epicranial aponeurosis is extremely thin. In the dog the occipital muscle occupies the superior part of the head; it overlies the temporal muscle.
With regard to the frontal muscle, which is of great extent in the ox ([Fig. 91], F), it is represented in the horse and the carnivora by a small fleshy fasciculus only, the fronto-palpebral muscle, similar to the superciliary muscle. This, occupying the superior and internal part of the border of the orbit, ends by blending its fibres with those of the orbicular muscle of the eyelids at the region of the eyebrow.
Orbicularis Palpebrarum ([Fig. 90], 2; [Figs. 91], [92]).—This annular muscle surrounds the palpebral orifice, and takes its origin on the internal part of the orbital region. In the horse it arises, by a small tendon, from a tubercle which occupies the external surface of the os unguis, or lachrymal bone.
This muscle determines the narrowing and closure of the palpebral orifice.
Pyramidalis Nasi.—The pyramidal muscle is not found in the domestic animals. It appears to be blended with the internal elevator of the upper lip and wing of the nose; this is easy of comprehension if we bear in mind the relative position of these two muscles in the human species.
Fig. 90.—Myology of the Dog: Muscles of the Head.
1, Masseter; 2, orbicularis palpebrarum; 3, zygomaticus major; 4, lachrymal (this muscle is sometimes described under the name of the small zygomatic); 5, levator labii superioris proprius; 6, levator labii superioris alæque nasi; 7, caninus; 9, buccinator; 11, zygomatico-auricularis; 12, external temporo-auricularis; 14, parotid gland; 15, parotido-auricularis; 16, inferior maxillary bone; 17, digastric.
Corrugator Supercilii.—This muscle is represented by the fronto-palpebral muscle noticed above, which is by some regarded as a vestige of the frontal.