In connection with other quadrupeds, it is described by certain authors as a very thin muscle, arising below the cavity of the orbit, where it is blended with the fibres of the internal elevator of the upper lip and the ala of the nose; thence it proceeds to terminate below by uniting with the subcutaneous muscle. But this muscle is regarded by other authors as the lachrymal muscle, which does not exist in this state in man, but of which the development is particularly remarkable, as to extent, in the ox, in which it descends as far as the buccinator.
According to other authors, some of the fibres of this muscle const.i.tute the small zygomatic.
[Ill.u.s.tration: FIG. 91.--MYOLOGY OF THE OX: MUSCLES OF THE HEAD.
1, Ma.s.seter; 2, orbicularis palpebrarum; F, frontalis; 3, zygomaticus major; 4, lachrymal (this muscle is sometimes described under the name of small zygomatic); 5, levator labii superioris proprius; 6, levator labii superioris alaeque nasi; 7, levator anguli oris or caninus; 8, orbicularis oris; 9, buccinator; 10, maxillo-l.a.b.i.al; 11, zygomatico-auricularis; 12, external temporo-auricularis; 14, parotid gland; 15, parotido-auricularis; 16, inferior maxillary bone.]
=Levator Labii Superioris Proprius= (Fig. 90, 5; Figs. 91, 92).--Also named by veterinarians the _supramaxillo-l.a.b.i.al_, or again, the _proper elevator of the upper lip_, this muscle arises from the external surface of the superior maxillary bone, pa.s.ses under the superficial elevator, which we shall study in the succeeding paragraph, and goes to be inserted into the thickness of the lip, to which its name indicates that it belongs.
The peculiarities of this muscle in different animals are the following:
In the dog and the cat it arises behind the infra-orbital foramen.
In the pig it arises from a depression below the orbital cavity, and its fleshy body is terminated in front by a strong tendon in the upper part of the snout, in which it divides into fasciculi.
In the ox it arises from the maxillary spine.
In the horse it arises below the orbital cavity; then, after having crossed the superficial elevator, it ends in a tendinous expansion, situated in the median line between the nasal fossae. This expansion divides into fasciculi, which end in the thickness of the upper lip.
By the contraction of this muscle, the lip is raised, on one side only, if a single muscle contracts, or in its whole extent, if the two muscles act simultaneously.
=Internal Elevator (or Superficial) of the Upper Lip and the Wing of the Nose= (_levator labii superioris alaeque nasi_) (Fig. 90, 6; Figs. 91, 92).--This is the muscle veterinarians designate _the supranaso-l.a.b.i.al_.
Arising from the frontal and nasal bones, it thence pa.s.ses towards the upper lip, where it is inserted as well as into the wing of the nose.
In the ox it is united above with the frontal muscle, and below is divided into two fasciculi, between which pa.s.s the elevator described above and the canine muscle.
In the horse it is also divided into two fasciculi; but the arrangement is the opposite as regards, their relations with neighbouring muscles, in this animal and in the preceding.
In the ox the external fasciculus is covered by the external elevator and the canine, which pa.s.s under the internal fasciculus; in the horse the deep elevator pa.s.ses under the two fasciculi, and the canine pa.s.ses under the external bundle, and afterwards covers the internal.
In the pig, the internal elevator is wanting.
As its name indicates, it raises the upper lip and the wing of the nose.
=Transversus Nasi.=--In the horse this muscle, which is very thin, is situated on the dorsum of the nose, and proceeds to be inserted into the cartilaginous skeleton of the nostrils. In the pig, it occupies an a.n.a.logous situation. It does not exist in the ox or in carnivora. The transversus nasi is a dilator of the nostrils.
[Ill.u.s.tration: FIG. 92.--MYOLOGY OF THE HORSE: MUSCLES OF THE HEAD.
1, Ma.s.seter; 2, orbicularis palpebrarum; 3, zygomaticus major; 4, lachrymal (this muscle is sometimes described under the name of the small zygomatic); 5, external elevator (or deep) of the upper lip and ala of the nose; 6, internal elevator (or superficial) of the upper lip and of the ala of the nose; 7, levator anguli oris or caninus; 8, orbicularis oris; 9, buccinator; 10, maxillo-l.a.b.i.alis; 11, zygomatico-auricularis; 12, temporo-auricularis externus; 13, cervico-auricularis; 14, parotid gland; 15, parotido-auricularis; 16, inferior maxillary bone.]
=Caninus= (Fig. 90; Figs. 7, 91, 92).--This is the muscle called by veterinarians _the great supramaxillo-nasal_.
In the dog and the cat it is situated below the inferior border of the external elevator of the upper lip, of which it follows the direction.
It arises, as does this latter, from the external surface of the maxilla, and goes also to terminate in the upper lip by blending with the internal elevator of this lip and of the alae of the nose. It raises the upper lip.
In the ox, it arises from the maxillary spine, and then divides into three parts; the superior pa.s.ses under the internal portion of the internal elevator of the upper lip and the alae of the nose, and goes into the nostril; whilst the two others, situated lower down, terminate in the upper lip.
In the pig, it is formed of two superimposed fasciculi, which arise from the spine of the maxilla and the impressions in front of it. These two fasciculi terminate in the snout, which they move laterally.
In the horse, it is situated at a certain distance from the external elevator; in the preceding animals it is in contact with the latter.
Arising behind from the external surface of the maxilla, in front of the maxillary spine, it is directed towards the anterior part of the face, pa.s.ses under the external portion of the internal elevator (it is the opposite of this in the ox), and proceeds, on expanding, to terminate in the skin of the nostril. By its contraction it dilates the latter.
=Orbicularis Oris= (Fig. 91, 8; Fig. 92).--This muscle, very fleshy in the solipeds and the ruminants, is arranged as a ring round the buccal orifice, in the thickness of the lips, where it is blended with the other muscles of this region.
Having for its function the narrowing of the orifice it surrounds, it acts during suction and in the prehension of food.
=Triangularis Oris.=--This muscle does not exist in domestic quadrupeds.
=Quadratus Menti.=--In the pig and the carnivora, it arises from the anterior part of the body of the inferior maxillary bone, and pa.s.ses at the other end to terminate in the corresponding portion of the lower lip, which it depresses by its contraction.
In the ox and the horse this muscle does not exist; it is replaced for the depression of the lower lip, which it affects in other animals, by supplemental fibres of the buccinator.
=The Prominence of the Chin.=--Below the lower lip in the horse is situated the so-called _prominence of the chin_, limited posteriorly by the _beard_, a depressed region which gives point to the curb of the bridle.
The prominence, which also exists in the ox, is a fibro-muscular pad which blends with the orbicular muscle of the lips, and receives on its superior aspect the insertion of the two muscles (_levator menti_) by which it is suspended. These arise, above, on each side of the symphysis of the inferior maxillary bone. They raise the lower lip with force, and they are the agents which, as we can sometimes observe in the horse, make it click against the upper lip, suddenly projecting it upwards.
This action sometimes becomes a habit, and its continuance const.i.tutes a vice.
A corresponding structure is found in the pig and in the carnivora, but in them it does not produce an external prominence such as we have described.
=Buccinator= (Fig. 90, 9; Figs. 91, 92).--Further designated by the name of _alveolo-l.a.b.i.al_, this muscle is situated on the lateral portions of the face, in the thickness of the cheeks. It consists of two layers, one superficial and the other deep.
The deep portion arises from the portion of the alveolar border of the superior maxillary bone which corresponds to the molar teeth, and from the anterior border of the ramus of the mandible. Thence it is directed forwards, pa.s.ses under the superficial layer, and blends with the fibres of the orbicular muscle of the lips. To this part of the buccinator some authors give the name of molar muscle.
The superficial portion is formed by fibres which pa.s.s from the alveolar border of the superior maxillary bone to the corresponding border of the opposite bone. It is very highly developed in the herbivora.
This muscle acts especially during mastication; it serves to press back again under the molar teeth the portions of food which fall outside the dental arch.
In the pig, the ox, and the horse, a muscle which is considered as supplemental to the buccinator is placed along the inferior border of the latter.
This muscle, which we describe separately under the names of _maxillo-l.a.b.i.alis_ (Fig. 91, 10; Fig. 92) and _depressor of the lower lip_, is clearly distinct from the buccinator, especially in the horse.
It arises, behind, with the deep layer of the muscle to which it is annexed, from the anterior border of the ramus of the lower jaw; in front it terminates in the thickness of the lower lip.
In the ox, it is more intimately united with the buccinator.
It depresses the lip to which it is attached, and displaces it laterally when it acts on one side only.
In the human species, the pinna of the ear being generally immobile, the muscles which belong to it are, very naturally, considerably atrophied.
Accordingly, the auricular muscles, anterior, superior, and posterior, are reduced to pale and thin fleshy lamellae, whose action is revealed in certain individuals, only in a way which may be said to be abnormal.
It is not the same in quadrupeds. The pinna of the ear is extremely mobile, and its displacements have a real value from the point of view of physiognomical expression. It is therefore necessary to review the muscles which move this pinna without giving them, at the same time, more importance than they merit, since in themselves they do not determine the formation of surface reliefs, which are sufficiently apparent.
Notwithstanding that for certain of these muscles it is possible to trace their a.n.a.logy with those of the auricular region of man, it is very difficult, because of their complexity, to trace this a.n.a.logy for all. This is why we shall not be able here, as we have done for the other muscles of the subcutaneous layer, to give at the head of each paragraph the name of a human muscle, and then to group in the same paragraph the muscles which correspond to it in different quadrupeds.
Therefore the nomenclature and the divisions adopted for these latter must serve us as a base or starting-point.
Because the pinna of the horse"s ear is so very mobile, we will first begin with a study of its auricular muscles.
=Zygomatico-auricularis= (Fig. 92, 11).--This muscle, which is formed of two small bands of fleshy fibres, arises from the zygomatic arch in blending with the orbicular muscle of the eyelids; thence it is directed towards the base of the pinna of the ear, and is inserted into this base, and also into the cartilaginous plate situated in front of and internal to this, and resting on the surface of the temporal muscle; this is the scutiform cartilage.