Artistic Anatomy of Animals Part 29

The zygomatico-auricularis, which we look on as the h.o.m.ologue of the anterior auricular of man, draws the pinna of the ear forwards.

=Temporo-auricularis Externus= (Fig. 92, 12).--This, which is thin and very broad, covers the temporal muscle.

It arises from the whole extent of the parietal crest, blending in this plane, in its posterior half, with the muscle of the opposite side.

Thence it is directed outwards towards the pinna of the ear, and is inserted into the internal border of the scutiform cartilage and on the inner side of the concha--that is to say, of the conchinian cartilage--which forms the princ.i.p.al part of the pinna. We are supposing, in the description of the muscles which move it, that this pinna has its opening directed outwards.

The external temporo-auricular, which recalls, from its situation, the superior auricular of man, is an adductor of the ear; besides, it causes it to describe a movement of rotation from without inwards, so as to direct its opening forwards.

=Scuto-auricularis Externus.=--This muscle may be considered as supplementary to the external temporo-auricular; the concha fasciculus of this latter partly covers it.

Extending from the scutiform cartilage to the inner side of the concha, it contributes to the movement of rotation by which the opening of the pinna of the ear is directed forwards.

=Cervico-auricular Muscles= (Fig. 92, 13).--These muscles, three in number, are situated behind the pinna of the ear; they are called, from their mode of superposition, the superficial, middle, and deep.

These arise, all three, from the superior cervical ligament, and pa.s.s from there towards the cartilage of the concha. They recall, as regards situation, the posterior auricular muscle of man.

=Superficial Cervico-auricular= (_Cervico-auricularis superioris_).--This muscle, inserted into the posterior surface of the concha, draws this cartilage backwards and downwards.

=Middle Cervico-auricular= (_Cervico-auricularis medius_).--Situated between the two other muscles of the same group, it proceeds, after having covered the superior extremity of the parotid gland, to be inserted into the external part of the base of the concha. It determines the rotation of this concha in such a way as to direct the opening of the ear backwards.

=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 pa.s.ses 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 pinnae 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 a.n.a.logous 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, p.r.i.c.ks 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 pinnae of the ears, these being caused by the folding of the integument, whilst the pinnae approach one another. These movements, with which are a.s.sociated fixation of look and a widening of the palpebral fissure, produce a peculiarly expressive look; this is why they merit our attention.

=Zygomatico-auricularis= (Fig. 90, 11).--Arises from the internal surface of the great zygomatic, pa.s.ses towards the pinna of the ear, and goes to be inserted into the external part of the base of the pinna, below its opening, to a prominence which corresponds to the ant.i.tragus of the human ear. It is to this ant.i.tragus, but proceeding from another direction, that the parotido-auricular muscle is inserted (Fig. 90, 15).

With regard to the cervico-auriculars, they are all three present. The superior, or superficial, situated behind the interscutellar portion of the external temporo-auricular, has its origin on the median line of the neck; thence it pa.s.ses towards the pinna of the ear, blending its fibres with those of the interscutellar muscle, and is inserted into the scutiform cartilage and the internal surface of the pinna.

Such are the princ.i.p.al muscles of the ear in the carnivora; it would seem to us superfluous to dwell on the others of this region, so that we will here conclude the study of the muscles in general, and that of the myology of the head in particular.

CHAPTER III

EPIDERMIC PRODUCTS OF THE TERMINAL EXTREMITIES OF THE FORE AND HIND LIMBS

We will first recall to mind that among the quadrupeds some are found of which the fingers and toes have their third phalanges terminated by claws--these are the unguiculates; and that in others the terminal extremity of each limb is completely encased in a h.o.r.n.y envelope, the hoof--these are the ungulates.

In the first group, the claws remind us to a certain extent of the arrangement of the nails in man; the inferior aspect of the paws is covered by an epidermic layer, thick and protective, which may be likened to the skin, correspondingly thick, which covers in the greater part of its extent the plantar surface of the foot in the human species.

In the second group, the surface by which the third phalanx rests on the ground is correspondingly protected, but this time by a layer of horn which belongs to the hoof.

After the preceding remarks, our study will be found to fall into a natural division, and it is in the order which we have just followed for the purpose of indicating its existence that we now proceed to study the nature and form of the different elements which complete or protect the digital extremities of the thoracic and abdominal limbs.

=Claws.=--These h.o.r.n.y coverings of the third phalanges, which we have to consider only in the dog and cat, may be compared with the nails of man, with which, however, they present, as is well understood, characteristic differences.

The claws are compressed laterally, curved on themselves, and are terminated in front by a sharp point in the felide, but more blunted in the dog. Their superior border is convex and thick. We may say, therefore, that a claw is a sort of hollow tube, in the form of a cone flattened in the transverse direction, in which the third phalanx is set, and which is itself set in a groove formed by a kind of osseous hood which occupies the base of this third phalanx (see Fig. 37, p. 57).

This definition is exact, as regards the general appearance; but, when more closely scrutinized, it is not sufficient. The tube in question is not formed of a single piece; each of the claws is formed by a lamina laterally folded, but of which the borders are not exactly joined together inferiorly; they leave between them a small interval, and this is filled by a layer of more friable h.o.r.n.y substance, to which has been given the name of plantar nail. This arrangement, which is clearly defined in the dog (Fig. 93), is comparable to that which we shall afterwards meet with in connection with the sole of the hoof of the horse (see Fig. 100, p. 257). In the dog and the cat, the weight of the limb resting on the inferior surface of the phalanges, it was necessary that the region of the plantar surface of the foot corresponding to these latter should be protected; this is the function of certain fibro-adipose pads, which are situated there, and which are designated by the name of _plantar tubercles_.

=Plantar Tubercles= (Fig. 94).--These tubercles, or dermic cushions, are divided, in each paw, into _tubercles of the digits_ (or of the toes), a _plantar tubercle_, and, on the fore-limbs, a _tubercle of the carpus_.

The tubercles of the fingers (or of the toes) are of the same number as the latter. That which belongs to the thumb is but little developed, but the others are more so. They are in relation with the plantar surfaces of the second and third phalanges, so that when the paw is in contact with the ground the articulation which, in each of the fingers or toes, joins these phalanges, rests on the corresponding pad.

The plantar tubercle is larger than the preceding. It is of a more or less rounded form; sometimes it is triangular, and then comparable in outline to the ace of hearts, the point of which is, in this case, turned towards the claws; its margin being sometimes strongly indented, it may also have a trilobate form. It is on it that rest the metacarpo-phalangeal or metatarso-phalangeal articulations, according to the limb studied. The tubercle of the carpus, situated at the level of the posterior surface of this latter, is less important than the preceding, the region which it occupies not reaching the ground during walking. But it is not to be neglected from the point of view of external form, because of the prominence which it produces.

[Ill.u.s.tration: FIG. 93.--CLAW OF THE DOG: INFERIOR SURFACE.

1, h.o.r.n.y lamina of the claw; 2, plantar nail; 3, tubercle of the corresponding digit.]

[Ill.u.s.tration: FIG. 94.--LEFT HAND OF THE DOG: INFERIOR SURFACE, PLANTAR TUBERCLES.

1, 1, 1, 1, 1, Tubercles of the fingers; 2, plantar tubercle; 3, tubercle of the carpus.]

In the ungulates the terminal extremity of the limb is, as we have above pointed out, enclosed in a h.o.r.n.y envelope which is no other than the hoof.

We will first study the hoof of the horse--a hoof which is single for each of the limbs, inasmuch as in this animal each of these has but a single digit.

=Hoofs of the Solipeds.=--We will first study the hoof as regarded in a general way--that is, without taking into account the limb to which it belongs. We will afterwards point out the differences presented when the hoofs of the fore and hind limbs are compared.

In connection with the external forms of the horse, the study which we are now commencing is of great importance. But, before entering upon it, it appears to us necessary to rapidly examine what the hoof contains (Fig. 95).

[Ill.u.s.tration: FIG. 95.--VERTICAL ANTERO-POSTERIOR SECTION OF THE FOOT OF A HORSE.

1, Third phalanx; 2, fibro-cartilage; 3, podophyllous tissue; 4, inferior part of the wall; 5, section of the wall of the hoof; 6, cutigerous cavity; 7, tendon of the anterior extensor of the phalanges; 8, reinforcing band coming from the suspensory ligament of the fetlock; 9, tendon of the superficial flexor of the phalanges; 10, tendon of the deep flexor of the phalanges.]

In the interior of this h.o.r.n.y box we find the third phalanx, a small sesamoid bone placed opposite to the posterior border of the latter, a portion of the inferior extremity of the second phalanx, and the tendons, which terminate at this region.

To the third phalanx are added two fibro-cartilaginous plates, flattened laterally, which prolong backwards the bone to which they are annexed.