[Illustration: 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.
=Zygomaticus Major= (Fig. 90, 3; Figs. 91, 92).--This is the _zygomatic-labial_ of veterinarians. This muscle is of an elongated form, and has a ribbon-like aspect.
In the dog and the cat it arises from the base of the pinna of the ear, from the portion of this base which bears the name of scutiform cartilage. (With regard to this cartilage, see p. 242, =Zygomatico-auricularis=.) From this it is directed downwards and forwards, to terminate, after having crossed the masseter, on the deep surface of the skin of the corresponding labial commissure.
This mode of termination is the same in the ox and the horse; but where the muscle differs is at the level of its upper extremity. There it ascends less than in the carnivora. In the ox it arises from the zygomatic arch in the neighbourhood of the temporo-maxillary articulation; in the pig and the horse its origin is still lower, on the surface of the masseter, close to the maxillary spine.
When it contracts, it draws upwards the labial commissure.
Now, in man, we remember, it is the great zygomatic that, by an action of the same kind, determines the essential characters of the expression of laughing.
There is, accordingly, a connection to be established between those displacements which are similar and the analogy of facial expression which necessarily results from them.[33]
[33] Édouard Cuyer, 'The Mimic,' Paris, 1802.
=Zygomaticus Minor= (Fig. 90, 4; Figs. 91, 92).--The existence of this muscle has not been clearly demonstrated. Nevertheless, Straus-Durckheim noted its presence in the horse, and described it as 'a muscle arising by two heads, of which one, the superior, arises from the malar bone below the orbit, and passes downwards and forwards over the fibro-adipose layer which supports the moustache. The second, the inferior, arises from the alveolar border in front of the second molar tooth, and passes forward to be inserted into the same fibro-adipose layer.'[34]