Short Extensor of the Thumb= (_Extensor primi internodii pollicis_)
(Fig. 73, 14; Fig. 74, 19; Fig. 75, 20).--United one to the other in
man, blended in quadrupeds, they form in the latter the muscles to which
veterinary anatomists give the name of _oblique extensor of the
metacarpus_.
This muscle arises from the median portion of the skeleton of the
forearm. There it is covered by the common extensor of the digits and
that of the small digit (anterior extensor and lateral extensor of the
phalanges). Then, at the internal border of the first of these muscles,
it becomes superficial, passes downwards and inwards, crosses
superficially the anterior extensor of the metacarpus, reaches the
inferior extremity of the radius, and becomes lodged in the most
internal of the grooves situated on the anterior surface of this
extremity, passes on the internal side of the carpus, and is inserted
into the superior extremity of the most internal metacarpal--that is, to
the first metacarpal, or metacarpal of the thumb--in the dog and cat; to
the internal rudimentary metacarpal in the horse.
It is an extensor of the metacarpal into which it is inserted; but as,
if we recall the extreme examples given above, in the dog the first
metacarpal is not very mobile, and in the horse the internal rudimentary
metacarpal is absolutely fixed to the bone which it accompanies, it is
more exact to add that this muscle is principally an extensor of the
metacarpus as a whole.
And yet, in the cat and the dog, it is also able to adduct the first
metacarpal bone. It must be understood that this movement would be
abduction, if the hand could be placed in the position of complete
supination, as in the human species.
=Long Extensor of the Thumb= (_Extensor secundi internodii pollicis_)
=and Proper Extensor of the Index= (_Extensor indicis_).--These two
muscles are blended together by their fleshy bodies, so that the single
name of _proper extensor of the thumb and index_ is preferable. This
muscle is but of slight importance from our point of view, for it is
extremely atrophied, and so much the more as the number of the digits is
lessened.
It arises, as the preceding, from the skeleton of the forearm, and there
it is deeply placed. Below, towards the carpus, its tendinous part
becomes superficial, to end in the following manner:
In the carnivora, the tendon divides into two very slender parts, which
are inserted into the thumb and the index. In the pig, the tendon is
blended with that of the common extensor of the internal digits.
Finally, in the ox and the horse, it is sometimes regarded as being
blended with the common or anterior extensor of the phalanges. But to us
it appears more rational to say that it does not exist, which, moreover,
is explained by the digital simplification of the hand.
Internal and Posterior Region
=Pronator Teres= (Fig. 76, 8).--This muscle, as may easily be
understood, undergoes, as do the supinators, a degree of degeneration in
proportion to the loss of mobility of the radius on the ulna. In animals
in which the bones of the forearm are not fused it exists; in those, on
the other hand, in which this segment has become simply a supporting
column, it is not developed--at least, in a normal manner.
It is, consequently, found best marked in the dog and the cat.
Forming, as in man, the internal limit of the hollow of the elbow, the
pronator teres has a disposition analogous to that which characterizes
the corresponding muscle in the human species. It arises from the
epitrochlea (internal condyle), proceeds downwards and outwards, and is
inserted into the middle portion of the body of the radius.
It is into the hollow in front of the elbow, which this muscle
contributes to limit, that the biceps and the brachialis anticus dip.
In the pig and the ox it is atrophied.
In the horse it does not exist. We may, however, sometimes find it, but
in an abnormal form. We were able to demonstrate its presence in the
form of a fleshy tongue situated on the internal side of the elbow
(Fig. 78) in a horse which we dissected many years ago in the laboratory
of the School of Fine Arts. Moreover--and the fact seemed to us an
interesting one--the forearm to which the muscle belonged had an ulna of
relatively considerable development (Figs. 79 and 80).[29]
[29] Edouard Cuyer, 'Abnormal Length of the Ulna and Presence of a
Pronator Teres Muscle in a Horse' (_Bulletin de la Societe
d'Anthropologie_, Paris, 1887).
This muscle is a pronator.
=Flexor Carpi Radialis= (Fig. 76, 10; Fig. 77, 7).--Called by veterinary
anatomists _the internal flexor of the metacarpus_, this muscle, which
is found on the internal aspect of the forearm, is situated behind the
pronator teres when this muscle exists, whilst in the animals which are
deprived of the latter the flexor carpi radialis has in front of it the
internal border of the radius, which separates it from the anterior
extensor of the metacarpus.
It is necessary to add that the flexor carpi radialis is similarly
separated from the anterior extensor of the metacarpus by the internal
border of the radius in animals in which the pronator teres exists, but
then only in that part of the forearm which is situated below this
latter.
The flexor carpi radialis arises from the epitrochlea. Its fleshy body,
fusiform in shape, descends vertically, and terminates in a tendon on
the posterior surface of the bases of the second and third metacarpals
in the dog and the cat, on the metacarpal of the large internal digit in
the pig, on the internal side of the metacarpus in the ox, and on the
superior extremity of the internal rudimentary metacarpal in the horse.
We see clearly, in this latter, a superficial vein which, in the shape
of a strong cord, passes along the anterior border of the flexor carpi
radialis; it is the subcutaneous median or internal vein, which, forming
the continuation of the internal metacarpal vein, joins the venous
system of the arm, after having crossed obliquely the corresponding part
of the radius.
=Palmaris Longus.=--This muscle, which exists distinctly in some
animals, but whose absence is far from being rare in the human species,
is not developed as a distinct muscle in any of the domestic quadrupeds.
[Illustration: FIG. 76.--MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB,
INTERNAL ASPECT.
1, Biceps; 2, long extensor of the forearm (supplementary or accessory
muscle of the great dorsal); 3, triceps, long head; 4, triceps, internal
head; 5, olecranon; 6, epitrochlea (internal condyle); 7, radial
extensors (anterior extensor of the metacarpus); 8, pronator teres; 9,
radius; 10, flexor carpi radialis (internal flexor of the metacarpus);
11, anterior ulnar (oblique flexor of the metacarpus); 12, superficial
flexor of the digits; 13, deep flexor of the digits; 14, flexor longus
pollicis (radial fasciculus of the deep flexor of the digits); 15,
pisiform bone.]
And yet some authors announce its presence in the dog, and describe it
as becoming detached, in the form of a cylindrical bundle, from the
anterior surface of the fleshy mass of the deep flexor of the digits
(see p. 196) to proceed then by a tendon which divides into two parts,
to terminate in the palm of the hand, where it blends with the tendons
of the superficial flexor, which are destined for the third and fourth
digits.
These authors give to this muscle the name of _palmaris longus_, and
attribute to it the action of flexing the hand.
=Anterior Ulnar= (_Flexor carpi ulnaris_) (Fig. 73, 16; Fig. 76, 11;
Fig. 77, 8).--Called by veterinary anatomists the _oblique flexor of the
metacarpus_, or _internal ulnar_, this muscle occupies the internal part
of the posterior aspect of the forearm in the ox and the horse, while in
the dog it occupies rather the external part.
This difference arises from the fact that in this latter, as in man, the
anterior ulnar is separated from the flexor carpi radialis by an
interval in which we see, on the internal aspect of the forearm, just at
the level of the elbow, the flexors of the digits. This interval is so
much the wider as there is no palmaris muscle to subdivide its extent
(Fig. 81). In the horse, the interval in question does not exist. In
this animal, indeed, the anterior ulnar is in contact with the radial
flexor, so that this muscle can occupy only a region belonging rather to
the internal surface of the forearm (Fig. 82).
In the dog the anterior ulnar is in contact with the posterior ulnar.
This relation recalls that which is found in man, where the two muscles
are merely separated by the crest of the ulna (Fig. 81). But in the
horse, in which the anterior ulnar has, so to speak, slid towards the
internal aspect, this muscle is separated above from the posterior
ulnar, and it is in the interval separating these two muscles that we
are able to perceive, but this time at the back of the forearm, the
muscular mass of the flexors of the digits (Fig. 82).
[Illustration: FIG. 77.--MYOLOGY OF THE HORSE: ANTERIOR LIMB, LEFT SIDE,
INTERNAL ASPECT.
1, Long extensor of the forearm (supplementary or accessory muscle of
the latissimus dorsi); 2, radialis muscles (anterior extensor of the
metacarpus); 3, tendons of extensor ossis metacarpi pollicis extensor
primi internodii pollicis united (oblique extensor of the metacarpus);
4, tendon of extensor communis digitorum (anterior extensor of the
phalanges); 5, strengthening band from the suspensory ligament of the
fetlock; 6, internal surface of the radius; 7, flexor carpi radialis
(internal flexor of the metacarpus); 8, anterior ulnar (oblique flexor
of the metacarpus); 9, pisiform bone; 10, 10, tendon of the superficial
flexor of the digits (superficial flexor of the phalanges); 11, 11,
tendon of the deep flexor of the digits (deep flexor of the phalanges);
12, sesamoid prominence; 13, suspensory ligament of the fetlock; 14,
internal rudimentary metacarpal.]
The anterior ulnar arises above from the epitrochlea and the olecranon;
thence it is directed towards the carpus, to be inserted into the
pisiform bone. It proceeds therefore from the inner side of the elbow to
the outer side of the upper part of the hand; it consequently crosses
the posterior surface of the forearm obliquely. This is why, as we have
pointed out above, it receives the name of the oblique flexor of the
metacarpus.
It is not unprofitable to recall in this connection that there is an
internal flexor of the metacarpus, which is the flexor carpi radialis;
and an external flexor of the metacarpus, which is the posterior ulnar
(in human anatomy, extensor carpi ulnaris). It is between these two
muscles that we find the oblique flexor--the anterior ulnar which we
have just been studying.
This muscle flexes the hand on the forearm.
=Superficial Flexor of the Digits= (_Flexor digitorum sublimis_) (Fig.
76, 12; Fig. 77, 10, 10).--This muscle arises from the epitrochlea;
thence it passes towards the hand, becomes tendinous, passes in a groove
on the posterior aspect of the carpus, and terminates on the palmar
surface of the phalanges in furnishing a number of tendons proportioned
to the digital division of the hand. Whatever the number, to which we
will again refer, each tendon is attached to the second phalanx, after
bifurcating at the level of the first, so as to form a sort of ring,
destined to give passage to the corresponding tendon of the deep flexor.
This ring and this passage have gained for the muscle the name of
_perforated flexor_.
In the dog and the cat the principal tendon is divided into four parts,
which go to the four last digits.
In the ox it is divided into two parts only; as, moreover, in the pig,
whose superficial flexor is destined for the two large digits only, the
lateral digits receiving no part of it.
Finally, in the horse the tendon is single.
We have previously pointed out that in the carnivora this muscle is
visible on the internal and posterior aspects of the forearm, in the
interval which is limited in front by the flexor carpi radialis and
behind and outside by the anterior ulnar.
Certain details are still to be added to the description of this
muscle. We will enter on an analysis of them after we have given some
indications relative to the following muscle:
=Deep Flexor of the Digits= (_Flexor digitorum profundus_) (Fig. 75, 21,
22; Fig. 76, 12; Fig. 77, 11, 11).--This muscle is covered by the
superficial flexor. It arises from the epitrochlea, from the radius, and
from the ulna, either from the olecranon process--as in the ox, pig, and
horse--or from almost the whole extent of the shaft of the same bone, as
in the cat and dog.
[Illustration: FIG. 78.--LEFT ANTERIOR LIMB OF THE HORSE: INTERNAL
ASPECT.
1, Internal flexor of the metacarpus or great palmar; 2, inferior part
of the biceps; 3, inferior part of the brachialis anticus; 4, internal
lateral ligament of the elbow; 5, pronato teres muscle.]
The radial fasciculus represents in the domestic quadrupeds the long
proper flexor muscle of the thumb in man. For this reason we shall
describe the muscle afresh in the following paragraph:
The fleshy bundles of which we have just spoken terminate in a tendon
which afterwards divides into slips, the number of which is in
proportion to the digital division of the hand. These slips then pass
through the slit or _buttonhole_ in the tendon of the superficial
flexor, and proceed to terminate on the third phalanx; hence the name of
_perforating_, which is also given to the deep flexor of the digits.
In the dog and the cat the tendon is divided into five portions, each of
which proceeds to one of the digits. The internal tendon, which is
destined for the thumb, terminates on the second phalanx of this digit.
In the pig the tendon divides into four tendons destined for the four
digits.
In the ox there are but two tendons.
In the horse the tendon is single.
As their names indicate, these muscles, both superficial and deep, flex
the digits. In addition to this, they flex the hand on the forearm.
We mentioned above that certain details relative to the superficial
flexor must be analyzed in a special way. We now add that this should
also be done with regard to the deep flexor. The point in question is
the arrangement which the tendons of these muscles present at the level
of the palmar region of the hand.
It is easy, in the case of the dog or the cat, to picture to one's self
this arrangement, especially if we recollect that which exists in the
human species. The tendons of the flexors are placed on a kind of
muscular bed formed by the union of the muscles of the region, but,
moreover, from the point of view of external form, these tendons are not
of very great importance.
But in the ox and the horse it is quite otherwise. From the
simplification of the skeleton of the hand, and the reduction of the
number of movements which the bones that form it are able to execute,
there naturally results a diminution of its muscular apparatus. Apart
from the existence of muscular vestiges of but little importance, we can
say that, in reality, the hand does not possess any muscles. On its
palmar aspect are found only the tendons of the flexors of the digits,
and as these tendons are large, and the hand long, they give origin to
external forms which it is necessary to examine.
[Illustration: FIG. 79.--LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL
ASPECT.
1, Ulna of abnormal length.]
[Illustration: FIG. 80.--LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL
ASPECT.
1, Normal ulna.]
In the horse, which we take as a type, the tendons of the flexors, after
being retained in position at the carpus by a fibrous band, the _carpal
sheath_, which recalls the anterior annular ligament of the human
carpus, and having passed this region, descend vertically, remaining
separated from the posterior surface of the metacarpus, so that the skin
sinks slightly on the lateral parts in front of the thick cord which
these tendons form. This cord is known by the name of _tendon_.
The flexors then reach the fetlock, and occupy the groove formed by the
peculiar arrangement of the two large sesamoid bones. They are retained
in position at this level by a fibrous structure, which forms the
metacarpo-phalangeal sheath. They then reach the phalanges, being
directed obliquely downwards and forwards, as, moreover, the latter are
also inclined. Then the tendon of the superficial flexor divides into
two slips, which are inserted into the second phalanx, between which
slips passes the tendon of the deep flexor, which in its turn goes to be
inserted, in the form of an expansion, into the semilunar crest, by
which the inferior surface of the third phalanx is divided into two
parts.[30]
[30] See, as regards this crest, in the paragraph relative to the hoof
of the solipeds, the figures which represent the third phalanx,
viewed on its inferior surface (Figs. 101 and 102, p. 258).
The part which these tendons play is of great importance in the large
quadrupeds.
These tendons, in fact, in addition to the action determined by the
contraction of the fleshy fibres to which they succeed, maintain the
angle formed by the canon-bone and the phalangeal portion of the hand,
and prevent its effacement under the weight of the body during the time
of standing. Their strong development, and the position they occupy,
make this understood, without it being necessary to insist on it
further.
We mentioned above that the 'tendon' descends vertically from the carpus
towards the fetlocks. This is as it should be. But, in some horses, it
is oblique downwards and backwards, so that the canon, instead of being
of equal depth from before backwards in its whole length, is a little
narrower in its upper part.
This results from the fact that the tendons of the flexors, too firmly
bound by the carpal sheath, gradually separate as they pass from the
metacarpus, going to join the fetlock; hence the obliquity pointed out
above. This abnormality producing a deleterious result, in the sense
that the tendinous apparatus acts with less strength as an organ of
support, it constitutes a defect of conformation which is expressed by
saying that the tendon has 'failed.'
=Long Proper Flexor of the Thumb= (_Flexor longus pollicis_) (Fig. 76,
14).--As we have already pointed out, this muscle is represented in
quadrupeds by the radial bundle of the deep flexor of the digits, so
that the two muscles are in reality blended the one to the other. This
union is sometimes found, but only as an abnormality, in the human
species. We have met some examples of this in the course of our
dissections.
=Pronator Quadratus.=--This muscle conforms to the general law which we
have already pointed out in connection with those which have for their
action the rotation of the radius around the ulna. We remember, indeed,
that when the bones of the forearm are fused with one another, the
muscles which are destined to produce a mobility which has then become
impossible disappear at the same blow.
[Illustration: FIG. 81.--DIAGRAM OF THE POSTERIOR PART OF A TRANSVERSE
SECTION PASSING THROUGH THE MIDDLE OF THE LEFT FORE-LIMB OF THE DOG:
SURFACE OF THE INFERIOR SEGMENT OF THE SECTION.
1, Radius; 2, ulna; 3, posterior ulnar; 4, anterior ulnar; 5, great
palmar (_flexor carpi radialis_); 6, flexors of the digits.]
[Illustration: FIG. 82.--DIAGRAM OF A HORIZONTAL SECTION OF THE MIDDLE
OF THE FOREARM OF THE LEFT LEG OF THE HORSE: SURFACE OF THE INFERIOR
SEGMENT OF THE SECTION.
1, Radius; 2, ulna; 3, posterior ulnar; 4, anterior ulnar; 5, great
palmar (_flexor carpi radialis_); 6, flexors of the digits.]
For this cause we do not find the square pronator in either the ox or
the horse, but can demonstrate its presence in the dog and the cat.
It is very deeply situated. This is why, and also on account of the plan
which we have traced for ourselves, we will simply say that it is
situated on the postero-internal aspect of the skeleton of the forearm,
and that it extends from the ulna to the radius.
It seems to us, however, sufficiently interesting to add that, instead
of occupying, as in the human species, the inferior fourth of the two
bones, it extends, particularly in the dog, over their whole length,
with the exception of their superior and inferior extremities.
Muscles of the Hand
We will first recall that, in man, the palm of the hand is divided into
three regions: a median palmar region, which is occupied by the tendons
of the flexors of the digits, the lumbricales, and, deeply, by the
interosseous muscles; an external region, or thenar eminence, formed by
the muscles destined for the movements of the thumb; an internal region,
or hypothenar eminence, which contains the muscles proper to the small
digit and the palmar cutaneous muscle.
These muscles are found, more or less developed, in the dog and the cat.
In the ox and the horse we meet with no vestige of the muscles of the
thenar or hypothenar eminences. Nevertheless, in these animals we find
the muscles which belong to the central region of the palm. We refer to
the lumbricales and the interosseous.
Although this fact has no relation to the object of our study, it
appears to us interesting to announce that there are traces of the
lumbricales found in the solipeds. These muscles are represented by two
fleshy bundles, situated one on each side of the tendon of the deep
flexor, above the ring of the tendon of the superficial flexor. These
small muscles are continued as slender tendons, which become lost in the
fibrous tissue of the _spur_, which is the horny process situated at the
posterior part of the fetlock, and which is covered by the hairs, more
or less abundant, which constitute the _wisp_.
As for the interosseous muscles, they are represented by the _suspensory
ligament of the fetlock_, and by two other small muscles, tendinous
throughout, which are situated between the principal metacarpal and the
rudimentary ones.
The suspensory ligament of the fetlock is considered an interosseous
muscle, on account of the red fleshy striations which it contains, and
from certain relations which it forms with the tendon of the common
extensor of the digits or anterior extensor of the phalanges. This
ligament (Fig. 75, 26; Fig. 77, 13), which plays an important part in
the standing position as a support of the foot, is a fibrous band
situated between the tendons of the flexors of the digits and the
principal metacarpal. It arises above, from the second row of the
carpals, descends towards the fetlock, where it divides into two
branches, which are inserted into the large sesamoid bones. At the same
level, this ligament gives off two fibrous bands which, passing
downwards and forwards, join the tendon of the anterior extensor of the
phalanges, blending with it, after having each crossed one of the
lateral aspects of the pastern. We have already referred to these bands
(p. 183).
It is with these latter that are blended the long and slender tendons
which form in a great measure the two other interosseous muscles
previously described.
A ligament of the same kind is found in the ox (Fig. 74, 23).
MUSCLES OF THE POSTERIOR LIMBS
Muscles of the Pelvis
The muscles which specially interest us in this region, because of their
superficial position, are the gluteus maximus and the gluteus medius. As
for the gluteus minimus, it is deeply situated, and more or less sharply
marked off from the second of the preceding muscles.
Inasmuch as the gluteus medius is more simple in arrangement than the
maximus, and will aid us in arranging our ideas in connection with the
latter, it is with the study of it that we will commence.
=Gluteus Medius= (Fig. 68, 29; Fig. 69, 26; Fig. 70, 35).--This muscle,
as in man, occupies the external iliac fossa. But this latter being
directed differently in the digitigrades and the ungulates, as we have
pointed out in the section on osteology (see pp. 91 and 99), the muscle
in question has consequently not the same direction in the two groups of
animals, being turned outwards in the first, and upwards in the second.
It is the thickest of the glutei, and gives to the region which it
occupies a rounded form.
From the iliac fossa from which it arises the fleshy fibres are directed
towards the femur, to be inserted into the great trochanter. It is
covered by an aponeurosis, and in part by the great gluteal. It
completely covers the small gluteal, which veterinary anatomists
designate by the name of the _deep gluteal_.
In the carnivora it does not pass in front of the iliac crest, but, in
the ox, and more particularly in the horse, it is prolonged anteriorly,
and thus covers, to a certain extent, the muscles of the common mass.
When it contracts, taking its fixed point at the pelvis, the gluteus
medius extends the thigh, which it is also able to abduct. If, on the
other hand, its fixed point is on the femur, it acts on the trunk, which
it raises, producing oscillating movements of the pelvis. It contributes
in this way to the action of rearing. We also see it distinctly appear
by the prominence which it produces in the dog, which, according to the
time-honoured phrase, _fait le beau_.
=Gluteus Maximus= (Fig. 68, 28; Fig. 69, 25; Fig. 70, 33, 34).--The
great gluteal muscle, further designated in veterinary anatomy the
_superficial gluteal_, is proportionately less developed in quadrupeds
than in man. Indeed, in the latter, where it is of very great thickness,
its volume is due to the important function which it fulfils in
maintaining the biped attitude.
In quadrupeds it contributes to form the superficial part of the crupper
and the external surface of the thigh. It is divided into two parts: one
anterior, the other posterior.
With regard to this latter, it will be necessary to indicate how it has
been sometimes regarded, and to what portion of the muscular system in
man it corresponds. But we believe that it is better to see beforehand,
without any preconceived idea, how these two parts are arranged.
In the dog, the anterior portion of the gluteus maximus arises from the
sacrum, while some fibres situated further forward arise from the
surface of the gluteus medius, near the iliac spine, and from the tensor
of the fascia lata with which these fibres are blended. The posterior
portion, united to the preceding--that is to say, to those of its fibres
which arise from the sacrum--takes its origin from the first coccygeal
vertebra. These two portions are directed towards the femur, to be
inserted into the great trochanter, and to the external branch of the
superior bifurcation of the linea aspera.
In the cat, the posterior bundle is less definitely blended with the
anterior. By a long and slender tendon which, behind, turns around the
great trochanter, and passes along the surface of the fascia lata, it
proceeds to join the knee-cap.
In the pig, the posterior portion is much more developed.
In the horse, the anterior portion arises from the internal iliac spine
(posterior in man), from the external iliac spine (anterior in man),
and, between these two osseous points, from the aponeurosis, which
covers the gluteus medius. Between these two origins the muscle is
deeply grooved, so that the tendency is to divide into two portions,
each of which is directed towards one of the iliac angles. In this
groove the gluteus medius is to be seen.
The fleshy bundles converge, and are directed towards the external
aspect of the femur, to be inserted into the osseous prominence known as
the third trochanter, after passing beneath the fleshy fibres of the
posterior portion. The latter, which is more considerable than the
preceding portion, arises above from the sacral crest, from the
aponeurosis which envelops the coccygeal muscles, from the sacro-sciatic
ligament, and from the tuberosity of the ischium. From this origin it
passes downwards, expands, then, describing a curve with the convexity
behind, it becomes narrowed, and proceeds to be inserted by a deep
fasciculus into the third trochanter, to the fascia lata, and, lastly,
to the knee-cap by the inferior part of its tendon.
Above, its posterior border is covered by the semi-tendinosus;
interiorly, the same border is in relation with the biceps femoris.
In the ox, the two parts of the great gluteal muscle are blended
together.
The long and broad fleshy band which they form arises in a manner
corresponding to that which we have just indicated in connection with
the horse, except that it has no attachment to the femur. The fascia
lata adheres strongly to its anterior border for a considerable length.
The form of the superior border of the great gluteal muscle of this
animal differs from that of the analogous portion in the horse. This
difference results from the peculiar aspect which the corresponding
region of the pelvis presents, and from the fact that, in the ox, as the
semi-tendinosus does not cover the portion of the great gluteal which
arises from the tuberosity of the ischium, the attachments of this
muscle to the sacro-sciatic ligament are uncovered.
Its descending portion, as a whole, has a rectilinear form, and does not
form a curve such as we indicated in the case of the horse.
The anterior portion of the great gluteal flexes the thigh. As regards
the posterior portion, it extends the thigh, and abducts it.
The action of this latter portion is particularly interesting as regards
the horse, because of the great development of the muscular mass which
this region presents in this animal. If the muscle takes its fixed point
above, it acts, in the extension of the thigh during walking, by
projecting the trunk forward during the whole time that the hind-limb to
which it belongs is in contact with the ground. If, on the contrary, it
takes its fixed point below, it makes the pelvis describe a see-saw
movement, upwards and backwards, on the coxo-femoral articulation, and
so contributes to the action of rearing.
Now that we have a knowledge of the disposition of the great gluteal
muscle, the moment has come to inquire what is the signification of its
posterior portion. The action of the anterior part being clearly
comparable to the human great gluteal, there can be no doubt as regards
the homology of this portion, so we will not insist on it further.
Of the posterior portion it is wholly different, for it is the homologue
of a fleshy bundle annexed to the great gluteal of man, but which is not
developed except as an abnormality.
Indeed, we sometimes find, placed along the inferior border of the great
gluteal, a fleshy fasciculus, separated from this muscle by a slight
interspace. This fasciculus, long and narrow, takes origin from the
summit of the sacrum, or the coccyx, and goes to partake of the femoral
insertions of the muscle which it accompanies. We further note a muscle
of the same kind, and presenting the same aspect, which comes from the
tuberosity of the ischium. Notwithstanding the difference which exists,
it is this abnormal fasciculus of man which in the quadrupeds here
studied is considered as constituting the posterior portion of the great
gluteal.
Bourgelat, considering this posterior portion as belonging to the biceps
cruris, to which, it is true, it adheres, forms of them a muscle which
he designates under the name of the _long vastus_. The anterior
fasciculus of this long vastus is none other than the posterior portion
of the great gluteal which we have just been studying.
Muscles of the Thigh
These muscles are divided into three regions: posterior, anterior, and
internal.
In a corresponding manner to that which we described in connection with
the arm, the thigh is applied to the side of the trunk, and is free,
more or less, only at the level of the inferior part.
Further, by reason of this shortening of the femur, the great gluteal
muscle, which is elongated in the ox and the horse, for example,
occupies in part the region corresponding to that which in man is
occupied by the muscles of the thigh, which here are reduced in length.
In other words, they are not superposed, as in the human species, but
juxtaposed. This is what we will verify further on.
The thigh, as a whole, is flattened from without inwards, its transverse
diameter being less in extent than its antero-posterior. Its external
surface is slightly rounded; that is, of course, in quadrupeds with
sufficiently well-developed muscles. Its internal surface is known as
the _flat of the thigh_.
Muscles of the Posterior Region
It is not unprofitable to recall to mind what muscles form the
superficial layer of this region in the human being. They are the biceps
cruris, semi-tendinosus, and semi-membranosus. We now proceed to
discover their analogues in quadrupeds.
=Biceps Cruris= (Fig. 68, 30; Fig. 69, 27; Fig. 70, 36).--It is this
which, according to Bourgelat, forms the central and posterior portions
of the long vastus muscle which we have mentioned above.
We know that the biceps of man is so named from the two portions which
form its upper part. In domestic quadrupeds, and also in the majority of
the mammals, this muscle is reduced to a single portion, that which
comes from the pelvis. It is therefore the portion which arises from the
femur which does not exist. This condition is sometimes found as an
abnormality in the human species.
The biceps arises from the tuberosity of the ischium; hence it is
directed, widening as it goes, towards the leg, where it terminates by
an aponeurosis which blends with the fascia lata and the aponeurosis of
the leg, and then proceeds to be attached to the anterior border or
crest of the tibia. By its inferior portion it limits externally the
posterior region of the knee--the popliteal space.
A fibrous intersection traverses the biceps in its whole length, with
the result that the muscle looks as if formed of two portions, one of
which is situated in front of the other.
In the dog and the cat it also arises from the sacro-sciatic ligament.
At this level its contour is distinguishable from that which corresponds
to the gluteal muscles, so that we there find two prominences one above
the other. The superior is formed by the gluteal muscles; the inferior
corresponds to the tuberosity of the ischium. The two prominences are
separated by a depression, from which the biceps emerges. We draw
attention to this form, the character of which is so expressive of
energy in the carnivora.
In these animals the biceps is inserted, by its anterior fibres, into
the articulation of the knee, while in the rest of its extent it covers
in great measure by its aponeurosis the external aspect of the leg.
In the pig, the biceps is but slightly marked off from the posterior
part of the great gluteal. In the ox, the division between these two
muscles is a little more distinct.
In the horse, the sciatic origin of the biceps is covered by the
semi-tendinosus, so that it only becomes free lower down, to appear in
the space limited behind by the semi-tendinosus, and in front by the
posterior part of the gluteus maximus.
When the biceps contracts, taking its fixed point from above, it flexes
the leg and helps to extend the thigh. If, on the other hand, it takes
its fixed point from below, it lowers the ischium, makes the pelvis
undergo a see-saw movement, and acts thus in the movement of rearing. It
is sometimes called, on account of one of its actions, and the position
which it occupies, the 'external flexor, or peroneal muscle of the leg.'
=Semi-tendinosus= (Fig. 68, 31; Fig. 70, 37; Fig. 87, 1; Fig. 88, 1;
Fig. 89, 28).--This muscle forms the contour of the thigh posteriorly,
so that when the latter is viewed from the side, it is the
semi-tendinosus above all that forms the outline. But, as we shall soon
see, it is in this case more distinct above than below, because of the
deviation which it undergoes in order to occupy by its inferior part the
internal side of the leg.
In the dog, the cat, and the ox, the semi-tendinosus arises from the
tuberosity of the ischium only, as in the human species. In the pig, it
also takes origin higher up from the sacro-sciatic ligament and the
coccygeal aponeurosis. In the horse, it extends still further, for it is
also attached to the crest of the sacrum.
The indication of these origins is of importance from the point of view
of external form, and to convince ourselves of this it is sufficient to
compare, in the ox and the horse, the region of the pelvis situated
below the root of the tail. In the ox, whose semi-tendinosus arises from
the tuberosity of the ischium only, this region is depressed, and the
cavity which is formed at this level is limited behind by the
tuberosity, which we know is very thick and prominent above. This causes
the superior part of the crupper to be less oblique than in the horse.
This characteristic is more especially marked in the cow, the bull
having this region of a more rounded form.
In the horse, on account of the semi-tendinosus ascending to the coccyx,
and even to the sacrum, the depression in question does not exist, and
the presence of the tuberosity of the ischium is only slightly revealed.
Descending from the origin indicated above, and inclining more and more
inwards, the semi-tendinosus proceeds to blend with the aponeurosis of
the leg, to be inserted into the anterior border of the tibia, after
crossing over the internal surface of the latter. It forms the internal
boundary of the popliteal space.
When this muscle contracts, taking its fixed point at the pelvis, it
flexes the leg. If, on the other hand, it takes its fixed point at the
tibia, it makes the pelvis describe a see-saw movement, and acts
accordingly in the movement of rearing.
It is sometimes named the 'internal or tibial flexor of the leg,' in
opposition to the crural biceps, which, as stated above, is then the
external flexor of the same region.
=Semi-membranosus= (Fig. 68, 32; Fig. 87, 2; Fig. 88, 2).--This muscle,
situated on the inner side of the semi-tendinosus, can be seen only when
the thigh is regarded on its posterior aspect.
It is only by reason of the homology of situation with the corresponding
muscle in man that we give the name under which we are studying it;
indeed, its structure is different, for it does not present the long,
broad, aponeurotic tendon which, in its superior part, characterizes
this muscle in the human species.
It arises above from the inferior surface of the ischium, and from the
tuberosity of the same bone. In the pig, and especially in the horse, it
passes further upwards, to arise from the aponeurosis of the coccygeal
muscles. So that if we compare it with that of the ox, which does not
extend beyond the ischium, we find that it is associated with the
semi-tendinosus in determining the difference of aspect to which we have
already called attention in connection with the region of the pelvis
situated below the root of the tail.
The semi-membranosus is then directed downwards and forwards, to take
its place on the internal surface of the thigh, where it is partly
covered by the gracilis muscle. It is inserted in the following manner:
In the dog and the cat it is divided into two parts, anterior and
posterior. The first, the more developed, is attached to the internal
surface of the inferior extremity of the femur; the second to the
internal tuberosity of the tibia.
The same arrangement occurs in the ox.
In the horse it is inserted into the internal surface of the internal
condyle of the femur.
The semi-membranosus is an extensor of the thigh when it takes its fixed
point at the pelvis; it is also an adductor of the lower limb. If it
takes its fixed point below it assists in the action of rearing.
It is now necessary for us, especially as regards the horse, to add some
indications relative to the exterior forms of the region constituted by
the semi-membranosus and semi-tendinosus. These two muscles form, by
their union, a surface contour, slightly projecting and of elongated
form, which occupies the posterior border of the thigh, the contour
corresponding to the region known as the _buttock_, in spite of the
fact that none of the gluteal muscles take any part in the structure of
this region. But the appearances, to a certain extent, justify the
preservation of this name. Indeed, because of the groove which separates
the gluteal region of one side from that of the opposite side, and from
the position of the anal orifice in the superior part of this groove, we
may admit the name which, in hippology, has been given to this part of
the thigh.
In addition to the reasons just given, and which are justified
especially by the position occupied by the muscular mass formed by the
union of the two muscles, there is another which, this time, has a
relation to a certain detail of form. In the superior part of the
convexity, which the gluteal region describes in the greater part of its
extent, there is found a more salient point, greatly accentuated in lean
animals, due to the presence of the tuberosity of the ischium; it is the
_point_ or _angle of the buttock_. At this level, and near the median
line, the semi-membranosus, not aponeurotic, but fleshy, and even
thicker there than anywhere else, sometimes produces a sharply localized
prominence. And as this prominence is situated on the outer side of the
anal orifice, the resemblance to a small 'buttock' is still more marked.
In lean horses a deep groove separates the mass formed by the
semi-membranosus and semi-tendinosus from that of the other muscles of
the thigh situated more in front; this groove is known by a name which
in this case is remarkably expressive--that of the 'line of poverty.'
If we examine the gluteal region as a whole by looking at the thigh from
the side, we plainly see the graceful curve produced by the general
convexity above indicated. We return to this point, in order to add
that, in its lower part, this curve alters its character; that is to
say, it is replaced by a slight concavity. This, which is designated
under the name of _the fold of the buttock_, is situated close to the
level of articulation of the leg with the thigh-bone.
Muscles of the Anterior Region
First we recall that in man the anterior muscles of the thigh are: the
triceps cruris, the tensor of the fascia lata, and the sartorius.
=Triceps Cruris= (Fig. 8, 36; Fig. 69, 31; Fig. 70, 41; Fig. 84, 2; Fig.
87, 3; Fig. 88, 3).--This muscle, which occupies the greater part of the
space between the pelvis and the anterior aspect of the femur, consists
of three parts: an external, or vastus externus; an internal, or vastus
internus; and a median or long portion, or rectus femoris. This division
accordingly recalls that which characterizes the human triceps cruris.
Furthermore, as in the case of the latter, the vastus externus and the
vastus internus take their origin from the shaft of the femur, while the
long portion arises from the pelvis. The _vastus externus_ arises from
the external lip of the linea aspera of the femur (or from the external
border of the posterior surface of this bone in the ox and the horse, in
which the linea aspera, considerably widened, especially in the latter,
forms a surface), and from the external surface of the shaft of the
femur. From this origin its fibres pass downwards and forwards, to be
inserted into the tendon of the long portion of the muscle and into the
patella.
In the dog and the cat the vastus externus is the most voluminous of the
three portions which constitute the triceps muscle. It is covered by the
fascia lata; but notwithstanding this, its presence is revealed by a
prominence which occupies the external surface of the thigh, and
surmounts, in the region of the knee, the more slightly developed one
which is produced by the knee-cap.
The _vastus internus_, situated on the inner surface of the thigh, takes
its origin from the corresponding surface of the femur, and proceeds
towards the patella.
The rectus femoris arises from the iliac bone, above the cotyloid
cavity; its fleshy body, which is fusiform, and situated in front of and
between the two vasti muscles, is directed towards the patella, into
which it is inserted by a tendon, which receives the other two
portions.
It is covered in front by the tensor of the fascia lata, and contributes
with the vastus externus to form the upper prominence of the knee.
The ligamentous fibres, which, as in man, unite the knee-cap to the
tibia, transmit to this latter the action determined by the contraction
of the triceps. This muscle is an extensor of the leg. Furthermore, the
rectus femoris, or long portion, acts as a flexor of the thigh.
=Tensor Fascia Lata= (Fig. 68, 34, 36; Fig. 69, 30, 31; Fig. 70,
40).--This muscle, generally larger in quadrupeds than in man, is flat
and triangular, and occupies the superior and anterior part of the
thigh.
It arises from the anterior iliac spine (inferior in carnivora, external
in the ox and the horse); it is prolonged downwards by an aponeurosis
(fascia lata) which occupies the external aspect of the thigh, proceeds
to be inserted into the patella and blend with the aponeurosis of the
biceps muscle.
It covers the rectus and vastus externus portions of the triceps cruris;
it is also in relation with the gluteal muscles.
The tensor of the fascia lata flexes the thigh, and serves to raise the
lower limb as a whole.
=Sartorius= (Fig. 68, 35; Fig. 87, 4, 5; Fig. 88, 5).--This muscle, long
and flattened, is called by veterinarians _the long adductor of the
leg_.
Before beginning the study of its position in quadrupeds, it is
necessary to remember that in man, where the thigh has a form almost
conical, the sartorius commences on the anterior face of this latter,
and is directed downwards and inwards to reach the internal surface of
the knee.
But now let us suppose the thigh flattened from without inwards; there
will evidently result from this a change in situation with regard to the
muscle in question. In fact, when this supposition is admitted, it is
easy to imagine that in a great part of the extent in which the
sartorius is normally anterior it will become internal. This is why,
these conditions being realized in quadrupeds, we shall find that, in
some of them, the sartorius is situated on the aspect of the thigh which
is turned to the side of the trunk.
In the dog and the cat it arises from the anterior iliac spine, and from
the half of the border of the bone situated immediately below it; but
the fibres from this second origin being hidden by the tensor of the
fascia lata, on the inner side of which they are situated, viewing the
external surface of the thigh, the muscle seems to arise from the iliac
spine only.
The sartorius in these animals is divided into two parts, which, in
general, are placed in contact. One of these fasciculi is anterior; the
other is situated further back. The first is visible on the anterior
border of the thigh, in front of the tensor of the fascia lata, but
below it inclines inwards; in its superior part also, a small extent of
the internal surface is occupied by it. The second, which, as we have
said, is situated further back, belongs wholly to the inner surface of
the thigh; it is this portion which arises from the inferior border of
the ilium (this is the homologue of the anterior border of the human
iliac bone).
The two fasciculi then pass towards the knee, being in relation with the
rectus and the vastus internus of the triceps. The anterior fasciculus
is inserted into the patella. The posterior unites with the tendons of
the gracilis (see below) and semi-tendinosus, and then proceeds to be
inserted into the superior part of the internal surface of the tibia.
On account of their different insertions these two parts receive the
names of _the patellar sartorius_ and _tibial sartorius_ respectively.
In the ox and the horse the sartorius is still more definitely situated
on the internal surface of the thigh. Consisting of a single fasciculus,
representing the tibial sartorius of the cat and the dog, it arises in
the abdominal cavity from the fascia covering the iliac muscle, then
passes under the crural arch, and terminates, by an aponeurosis which
blends with that of the gracilis, on the inner fibres of the patellar
ligament. In short, the sartorius is of interest to us in the carnivora
only, and especially on account of its anterior or patellar fasciculus.
It is an adductor of the leg and a flexor of the thigh.
Muscles of the Internal Region
The ilio-psoas pectineus and the adductors which we study in man, in
connection with the internal aspect of the thigh, offer little of
interest from the point of view of external form in quadrupeds; it is
for this reason that we will disregard them.
The gracilis alone merits description.
=Gracilis= (Fig. 87, 9; Fig. 88, 6).--Designated in veterinary anatomy
under the name of _the short adductor of the leg_, this muscle, expanded
in width, occupies the greater part of the internal surface of the
thigh, _or flat of the thigh_, as this region is also called. Let us
imagine, in man, the internal surface of the thigh broader, and the
internal rectus more expanded, and we shall have an idea of the same
muscle as it exists in quadrupeds.
The gracilis arises from the ischio-pubic symphysis and from the
neighbouring regions; thence it is directed towards the leg to be
inserted into the superior part of the internal surface of the tibia,
after being united to the tendons of the sartorius and semi-tendinosus.
We find, accordingly, at this level, an arrangement which recalls the
general appearance of what in man receives the name of _the goose's
foot_ (_pes anserinus_).
It is between this muscle and the sartorius, at the superior part of the
internal surface of the thigh, in the region which recalls the triangle
of Scarpa, that we are able, especially in the cat and the dog, to see
the adductor muscles of the thigh. We also partly see there, in these
animals, the vastus internus and the rectus of the triceps (see Fig.
87). The gracilis is an adductor of the thigh.
Muscles of the Leg
We will divide the leg into three regions: anterior, external, and
posterior. With regard to the internal region, there are no muscles
which belong exclusively to it; for it is in great measure formed by the
internal surface of the tibia, which, as in man, is subcutaneous.
Muscles of the Anterior Region
We first note that in the human species the tibialis anticus, extensor
proprius pollicis, extensor longus digitorum and the peroneous tertius
or anticus, form the subcutaneous layer of this region. We now proceed
to study these muscles in quadrupeds.
[Illustration: FIG. 83.--MYOLOGY OF THE HORSE: THE ANTERIOR TIBIAL
MUSCLE (FLEXOR OF THE METATARSUS), LEFT LEG, ANTERIOR VIEW.
1, Femoral trochlea; 2, tibia; 3, tendinous portion of the tibialis
anticus; 4, cuboid branch of same; 5, 5, its metatarsal branch; 6,
fleshy portion; 7, cuneiform branch of its tendon; 8, metatarsal branch
of the same tendon; 9, extensor longus digitorum (anterior extensor of
the phalanges turned outwards); 10, peroneus brevis (lateral extensor of
the phalanges).]
=Tibialis Anticus= (Fig. 83; Fig. 84, 6; Fig. 85, 4; Fig. 87, 10; Fig.
88, 10, 11).--It is further named by veterinarians the _flexor of the
metatarsus_.
In the dog and the cat this muscle, which is rather large, arises from
the external tuberosity of the tibia and from the crest of this bone. In
its superior part it is flat, but lower down it is thick and produces a
prominence in front of the tibia. Finally, it becomes tendinous, and
passes towards the tarsus; thence it is directed towards the inner side
of the metatarsus, and is inserted into the great-toe, this latter being
sometimes well developed, but also often merely represented by a small
bony nodule on which the muscle is then fixed.
In the other animals with which we here occupy ourselves, the tibialis
anticus presents a complexity which would be incomprehensible unless
this muscle be first studied in the horse.
In this latter the tibialis anticus consists of two distinct portions,
placed one in front of the other: a fleshy portion, and a tendinous
portion running parallel to it.
The muscle is covered, except on its internal part and inferiorly, by a
muscle with which we will occupy ourselves later on--that is, the common
extensor of the toes.
The tendinous portion of the tibialis anticus (Fig. 83), especially
covered by the extensor of the toes, arises from the inferior extremity
of the femur, from the fossa situated between the trochlea and the
external condyle; thence it descends towards a groove which is hollowed
out on the external tuberosity of the tibia, and is directed towards the
tarsus, where it divides into two branches, which are inserted into the
cuboid bone and the superior extremity of the principal metatarsal.
These two parts form a ring through which the terminal tendon of the
fleshy portion of the same muscle passes.
This fleshy portion, situated behind the preceding, arises from the
superior extremity of the tibia, on the borders of the groove in which
the tendinous portion lies; thence it passes downwards for a short
distance on the inner side of the common extensor of the toes, which
covers it in the rest of its extent. It ends in a tendon which, after
passing through the tendinous ring above noticed, divides into two
branches. One of these branches is inserted into the anterior surface
of the superior extremity of the principal metatarsal, the other into
the second cuneiform bone.
[Illustration: FIG. 84.--MYOLOGY OF THE DOG: LEFT HIND-LIMB, EXTERNAL
ASPECT.
1, Biceps cruris and fascia lata, divided in order to expose the upper
part of the muscles of the leg; 2, inferior portion of the triceps
cruris; 3, patella; 4, semi-tendinosus; 5, inferior extremity of the
femur; 6, tibialis anticus (flexor of the metatarsus); 7, extensor
longus digitorum (anterior extensor of the phalanges); 8, tibia; 9,
peroneus longus; 10, peroneus brevis; 11, fifth metatarsal; 12,
fasciculus detached from the peroneus brevis and passing towards the
fifth toe; 13, external head of gastrocnemius; 14, tendo-Achillis; 15,
calcaneum; 16, flexor digitorum sublimis; 17, 17, tendon of the flexor
digitorum sublimis; 18, flexor longus pollicis (portion of the deep
flexor of the toes); 19, dorsal muscle of the foot (short extensor of
the toes).]
In the ox the same two portions of the tibialis anticus exist, but with
this capital difference--that the anterior portion is fleshy,
superficial, and blended for a great part of its length with the common
extensor of the toes.
The portion which corresponds to that which is fleshy in the horse
arises from the tibia; below, it ends on the inner surface of the
superior extremity of the metatarsus and the cuneiform bones. That which
represents the tendinous part, which is also fleshy, as we have just
pointed out, arises above with the common extensor of the toes, from the
femur, in the fossa situated between the trochlea and the external
condyle; whilst below, after having given passage to the tendon of the
preceding portion, as in the horse, it is inserted into the metatarsus
and the cuneiform bones.
In the pig, the tibialis anticus presents an arrangement nearly similar
to that which we have just described.
It seems to us of interest to add that it has been sought to ascertain
to what muscle of the human leg the tendinous part of the tibialis of
the horse corresponds--a part which has become fleshy in the pig and the
ox.
According to some authors, it represents the peroneus tertius; but that
muscle is situated on the outer side of the common extensor of the toes;
and here the portion with which it has been compared is placed on the
inside. It has also been likened to a portion of the common extensor of
the toes, but it does not pass to the latter. Lastly, it has been
considered as being the homologue of the proper extensor of the
great-toe; but why, then, in the ox, which has no great-toe, is it so
highly developed? Nevertheless, its position and its relations
sufficiently warrant this method of comprehending it. The tibialis
anticus is a flexor of the foot. It is also able, in animals in which
the tarsal articulations allow of the movement, to rotate the foot
inwards.
[Illustration: FIG. 85.--MYOLOGY OF THE OX: LEFT LEG, EXTERNAL ASPECT.
1, Gluteus maximus and biceps cruris; 2, semi-tendinosus; 3, patella; 4,
tibialis anticus (flexor of the metatarsus); 5, extensor longus
digitorum (anterior extensor of the phalanges); 6, fasciculus of the
extensor longus digitorum, which is considered as the representative of
the tendinous portion of the tibialis anticus in the horse; 7, peroneus
longus; 8, peroneus brevis (proper extensor of the external toe); 9,
external head of gastrocnemius; 10, soleus; 11, tendo-Achillis; 12,
calcaneum; 13, tendon of the extensor longus digitorum (superficial
flexor of the phalanges); 14, flexor longus pollicis and tibialis
posticus (deep flexor of the phalanges); 15, tendon of the superficial
flexor of the toes; 16, tendon of the deep flexor of the toes; 17,
suspensory ligament of the fetlock.]
With regard to the tendinous part, called by veterinarians the _cord of
the flexor of the metatarsus_, it serves, in the horse, to produce the
flexion of the metatarsus when the knee is already flexed; it thus acts
in a passive fashion, which is explained by its resistance and the
position which it occupies in relation to these two articulations.
=Extensor Proprius Pollicis.=--This muscle exists only in the dog and
the cat, and there in a rudimentary condition.
It is covered by the common extensor of the toes and the tibialis
anticus, and passes, accompanied by the tendon of this latter muscle, to
terminate on the second metatarsal, or the phalanx, which articulates
with it. When the first toe exists in the dog, it is inserted into this
by a very slender tendon.
=Extensor Longus Digitorum= (Fig. 83, 9; Fig. 84, 7; Fig. 85, 5, 6; Fig.
86, 4; Fig. 87, 12; Fig. 88, 7).--It is also called by veterinarians
_the anterior extensor of the phalanges_.
In the dog and the cat this muscle is to be seen in the space limited
behind by the peroneus longus and in front by the tibialis anticus.
Above it is covered by this latter. In the lower half of the leg, it is
also in relation, on the inner side, with the tibialis anticus; but
behind it is separated from the peroneus longus by the external surface
of the shaft and inferior extremity of the tibia. This arrangement,
besides, recalls that which is found in man, the peroneus longus of the
latter diverging in the same way, at this level, from the common
extensor, and leaving exposed the corresponding portion of the skeleton
of the leg.
This muscle, fusiform in shape, arises at its upper part from the
external surface of the inferior extremity of the femur, then its tendon
passes into a groove hollowed on the external tuberosity of the tibia.
The fleshy body which succeeds is directed towards the tarsus, but
before reaching it is replaced by a tendon. This tendon, at the level of
the metatarsal bones, divides into four slips, which pass towards the
toes, and are inserted into the second and third phalanges of the
latter.
In the horse it covers, to a great extent, the tibialis anticus, so that
it is the latter which forms the large fusiform prominence especially
noticeable in the middle region, to which the contour of the anterior
surface of the leg is due.
[Illustration: FIG. 86.--MYOLOGY OF THE HORSE: LEFT HIND-LIMB, EXTERNAL
ASPECT.
1, Semi-tendinosus; 2, biceps cruris; 3, patella; 4, extensor longus
digitorum (anterior extensor of the phalanges); 5, reinforcing band
arising from the ligament of the fetlock; 6, peroneus brevis (lateral
extensor of the phalanges); 7, external head of gastrocnemius; 8,
soleus; 9, tendo-Achillis; 10, calcaneum; 11, tendon of the superficial
flexor of the toes (superficial flexor of the phalanges); 12, flexor
longus pollicis and tibialis posticus (deep flexor of the phalanges);
13, 13, tendon of the superficial flexor of the phalanges; 14, 14,
tendon of the deep flexor of the phalanges; 15, suspensory ligament of
the fetlock; 16, principal metatarsal: 17, external rudimentary
metatarsal.]
It arises above from the inferior extremity of the femur, from the fossa
situated between the trochlea and the external condyle; therefore, it
has a common origin with the tendinous portion of the tibialis anticus,
or flexor of the metatarsus.
The tendon, which at the level of the inferior part of the leg succeeds
to the fleshy body, passes in front of the tarsus, the principal
metatarsal, and receives the tendon of the peroneus brevis which we will
describe later on. It then reaches the anterior surface of the fetlock.
There it presents an arrangement analogous to that which we have pointed
out in connection with the anterior extensor of the phalanges--a muscle
which, in the fore-limbs, corresponds to the common extensor of the
digits; that is to say, it is inserted, in form of an expansion, into
the pyramidal prominence of the third phalanx, after having formed
attachments to the first and second, and having received on each side a
strengthening band from the suspensory ligament of the fetlock.
In the ox the long extensor of the toes is united above, and for a great
part of its length, with the portion of the tibialis anticus, which
represents, albeit in the fleshy state, the tendinous cord of the latter
in the horse.
In common with this portion, it arises from the inferior extremity of
the femur. Thence it passes towards the tarsus and divides into two
fasciculi, internal and external, which are continued by tendons. These
pass towards the phalanges, and, in case of the common extensor of the
digits belonging to the fore-limbs, the internal is destined for the
internal toe, and the external is common to the two toes.
[Illustration: FIG. 87.--MYOLOGY OF THE DOG: LEFT HIND-LIMB, INTERNAL
ASPECT.
1, Semi-tendinosus; 2, semi-membranosus; 3, triceps cruris (vastus
internus); 4, sartorius (patellar); 5, sartorius (tibial); 6, patella;
7, first or middle adductor; 8, small and great adductor united; 9,
gracilis; 10, tibialis anticus (flexor of the metatarsus); 11, tibia;
12, tendon of extensor longus digitorum (anterior extensor of the
phalanges): 13, gastrocnemius, inner head; 14, tendo-Achillis; 15,
calcaneum; 16, popliteus; 17, superficial flexor of the toes; 18, flexor
longus pollicis (portion of the deep flexor of the toes); 19, flexor
longus digitorum (portion of the deep flexor of the toes); 20, tendon of
the tibialis posticus.]
[Illustration: FIG. 88.--MYOLOGY OF THE HORSE: LEFT HIND-LEG, INTERNAL
ASPECT.
1, Semi-tendinosus; 2, semi-membranosus; 3, triceps cruris (vastus
internus); 4, patella; 5, sartorius; 6, gracilis; 7, extensor longus
digitorum common extensor of the toes (anterior extensor of the
phalanges); 8, tendon of the preceding muscle; 9, reinforcing band given
off by the suspensory ligament of the fetlock; 10, tibialis anticus
(flexor of the metatarsus), its tendinous portion; 11, tibialis anticus
(flexor of the metatarsus), its fleshy portion; 12, cuneiform branch of
the tendon of this fleshy portion; 13, internal head of gastrocnemius;
14, popliteus; 15, tendon of the flexor brevis digitorum (superficial
flexor of the phalanges); 16, flexor longus pollicis and tibialis
posticus (deep flexor of the phalanges); 17, flexor longus digitorum
(oblique flexor of the phalanges); 18, 18, tendon of the superficial
flexor of the phalanges; 19, 19, tendon of the deep flexor of the
phalanges; 20, suspensory ligament of the fetlock; 21, principal
metatarsal; 22, internal rudimentary metatarsal.]
In the pig the general arrangement of the muscle is similar, but the
tendons end in a manner which is a little more complicated. Apart from
the fasciculi which correspond to the tendinous portion of the tibialis
anticus (fleshy here, as in the ox), the long extensor of the toes at
the level of the tarsus divides into three tendons: the internal goes to
the great internal toe; the middle bifurcates in the upper part of the
digital portion of the foot, and each of its branches goes towards one
of the great-toes; the external divides to pass towards each of the two
small toes, and towards the great ones; but this latter disposition is
not constant.
By its contraction the muscle which we have just studied extends the
phalanges and flexes the foot.
=Peroneus Tertius.=--This muscle is not found in domestic quadrupeds.
We should remember, nevertheless, that certain authors consider as
representing it the tendinous portion of the anterior tibial of the
horse, or the corresponding portion now fleshy, of the same muscle in
the pig and the ox. It is by reason of this fact that it is called the
third peroneal, notwithstanding that in the numerical order of the
peroneals it is rather the first.
But that which still further complicates this question of nomenclature
is that some authors give this name of third to a peroneal which, in the
carnivora, is situated more definitely in the group of external muscles
(see below, =Short Lateral Peroneal=).
Muscles of the External Region
In man, two muscles constitute this region; they are the peroneus longus
and peroneus brevis.
=Peroneus Longus= (Fig. 84, 9; Fig. 85, 7).--This muscle does not exist
in the domestic animals; only in the flesh-eaters, the pig and the ox
excepted.
It is in relation superiorly with the tibialis anticus, and inferiorly
with the common extensor of the toes; in the ox, it is in contact with
this latter muscle throughout its whole length.
The peroneus longus arises from the external tuberosity of the tibia;
towards the middle of the leg it is replaced by a tendon. This proceeds
towards the tarsus, but previously it passes between the tibia and
fibula. In the ox it is situated in front of the coronoid tarsal bone;
we recollect that this bone is regarded as representing the inferior
extremity of the fibula (see p. 97). Then it passes into a groove
belonging to the cuboid bone or to the cuboido-scaphoid bone in the ox,
traverses obliquely the posterior aspect of the tarsus, and is inserted
into the rudimentary bone which represents the first toe; or, if this
does not exist, into the innermost of the metatarsal bones.
This muscle is an extensor of the foot. It also rotates it outwards in
the animals in which the articulation permits this latter movement.
=Peroneus Brevis= (Fig. 83, 8; Fig. 83, 10; Fig. 84, 10; Fig. 86,
6).--In the dog and the cat, this muscle is covered in part by the
peroneus longus, and arises from the inferior half of the tibia and the
fibula; at the level of the tarsus it becomes tendinous, passes into a
groove hollowed out on the external surface of the inferior extremity of
the fibula, and terminates on the external aspect of the superior
extremity of the fifth metatarsal. A little before this insertion it
crosses the tendon of the long peroneal in passing to the outer side of
the latter.
To the short peroneal muscle is found annexed a very thin fasciculus
which lies upon it. This fasciculus arises from beneath the head of the
fibula, and is soon replaced by a thin tendon, which, accompanying that
of the short peroneal, proceeds towards the foot, after having traversed
the groove in the inferior extremity of the fibula; passes along by the
fifth metatarsal (Fig. 84, 12); blends at the level of the first phalanx
of the fifth toe with the corresponding tendon of the long extensor of
the toes, and partakes of the insertions of this tendon.
This fasciculus is designated by some authors under the name of the
peroneal of the fifth toe, or the proper extensor of the same toe. But
what makes still further complications is that other authors regard it
as an anterior, or third, peroneal. Now, these names are those which
other anatomists have applied to the fasciculus of the anterior tibial,
which, in the pig and the ox, is fused in part with the long extensor of
the toes. Hence there results a confusion which is truly regrettable.
In brief, we can, without inconvenience, consider it as a fasciculus of
the short peroneal muscle.
We sometimes find in man, but abnormally, an arrangement which partly
recalls that which we have just indicated. It consists in a duplication
of the tendon of the short peroneal, one of the branches of which goes
to the fifth metatarsal, and the other to the fifth toe; it is sometimes
a single fasciculus which goes to the phalanges of this latter. We have
met with examples of these anomalies.[31] In the pig, the short peroneal
is situated on the same plane as the long. It consists of two clearly
distinct fasciculi, which arise from the fibula. The tendon of the
anterior fasciculus proceeds to the great external toe--that is to say,
the fourth, of which it is the proper extensor. The posterior fasciculus
terminates on the small external toe, the fifth, of which it is in like
manner the extensor.
[31] Edouard Cuyer, 'Anomalies, Osseous and Muscular' (_Bulletins de
la Societe d'Anthropologie_, Paris, 1891).
In the ox, the fleshy fibres of the short peroneal arise from a fibrous
band which replaces the fibula, and from the external tuberosity of the
tibia. Situated behind the long peroneal and on the same plane, it
terminates in a tendon which appears at the level of the inferior part
of the leg; it passes in front of the canon, and is inserted into the
external toe, of which it is the proper extensor.
In the horse, it is the sole representative of the peroneal muscles, and
veterinary anatomists have given it the name of _the lateral extensor of
the phalanges_.
Its fleshy body arises above from the external lateral ligament of the
knee-joint, and from the whole length of the fibula. In the middle third
of the leg it is narrowed; lower down it is replaced by a tendon. This
is lodged in a groove hollowed on the external surface of the inferior
extremity of the tibia; then after passing along the external surface of
the tarsus, it is directed forward, and proceeds to blend towards the
middle of the canon-bone with the tendon of the long extensor of the
toes, or anterior extensor of the phalanges, of which it shares the
insertions. It extends the phalanges into which it is inserted. It also
flexes the foot.
Muscles of the Posterior Region
It will not be unprofitable to recall to mind that, in man, the muscles
of this region are arranged in two layers: a superficial layer
consisting of the gastrocnemius and soleus, to which is added a muscle
of little importance, the plantaris, and a deep layer formed by four
muscles--the popliteus, flexor longus digitorum, tibialis posticus, and
flexor longus pollicis.
The gastrocnemius and soleus, independent in their upper portion, unite
below in a common tendon; they thus form also a triceps muscle, which we
designate under the name of the triceps of the leg, or triceps suralis,
because it forms the elevation of the calf of the leg (from _sura_,
calf).
=Gastrocnemius= (Fig. 83, 9, 11; Fig. 84, 13, 14; Fig. 86, 7, 9; Fig.
88, 13).--The external and internal heads of the gastrocnemius, distinct
from one another only in their upper portion, arise from the shaft of
the femur, above the condyles, on the borders of the popliteal surface,
to a relatively considerable extent in the great quadrupeds.
At this level they are situated in the popliteal region--that is to say,
in the space limited externally by the biceps, and internally by the
semi-tendinosus. But as they descend to a rather low level on the leg in
quadrupeds, and especially in carnivora, they do not, properly speaking,
determine a projection of the calf of the leg. However, they pass from
this region but to be soon continued by a tendon--the tendo-Achillis,
which is inserted into the calcaneum.
Now, the region of the tarsus is called by veterinarians _the ham_, the
posterior surface of which is angular, because of the oblique direction
of the leg with regard to the vertical direction of the metatarsus and
the presence of the calcaneum; the prominence which this surface
presents has received the name of _the point of the ham_, and the tendon
which ends there that of _the cord of the ham_.
But the tendo-Achillis does not alone form this cord. Indeed, as we will
soon see, the tendon of the superficial flexor of the toes takes part in
its formation.
We may add, with regard to the tendo-Achillis, that it is more clearly
perceived as an external feature, because the skin sinks in front of it,
as it does in man, over the lateral parts of the region which it
occupies.
The gastrocnemius, when it contracts, extends the foot on the leg.
It serves to maintain the tibio-tarsal angle in the standing position,
and during walking, to determine the steadying of the hind-limbs, which
then, after the fashion of a spring, project the body forward.
By an analogous movement they take part in the posterior projection of
the hind-limbs in the act of kicking; but they are not the only ones to
act in this case, the muscles of the buttock and thigh also being
brought into play.
=Soleus= (Fig. 83, 10; Fig. 86, 8).--This muscle, much less developed in
quadrupeds than in man, does not exist in the dog.
With regard to the soleus in the pig, Professor Lesbre says: 'Meckel
denied its existence; we, however, believe that it is united to the
external head of the gastrocnemius, its origin being transferred to the
femur.'[32]
[32] F. X. Lesbre, 'Essai de Myologie comparee de l'homme et des
mammiferes domestiques en vue d'etablir une nomenclature unique
et rationelle,' Lyon, 1897, p. 169.
But in animals in which it exists, this muscle, of but little
importance, occupies the outer side of the leg. It arises above from the
external tuberosity of the tibia, and terminates below in a tendon which
is united with that of the gastrocnemius.
The soleus has the same action as these latter.
=Plantaris.=--In quadrupeds this muscle is blended with the superficial
flexor of the toes, which we will study afterwards.
=Popliteus= (Fig. 87, 16; Fig. 88, 14).--In man, this muscle, which
occupies the posterior surface of the tibia, above the oblique line, is
completely covered by the gastrocnemius.
In quadrupeds, where it is more voluminous, it projects internally
beyond the gastrocnemius, so that it is seen in the internal and
superior part of the region of the superficial layer of muscles,
immediately behind the internal surface of the tibia, which, as we know,
is subcutaneous.
The popliteus arises from the external surface of the external condyle
of the femur. Thence its fibres which diverge pass to be inserted into
the superior part of the posterior surface and of the internal border of
the tibia. It is in this latter region that it projects beyond the
gastrocnemius, but we may add that there it is more or less covered by
the semi-tendinosus.
It flexes the leg, and rotates it forwards.
=Superficial Flexor of the Toes= (Fig. 83, 13, 15; Fig. 84, 17; Fig. 86,
11, 13, 13; Fig. 87, 17; Fig. 88, 15, 18, 18).--In man, the homologue of
this muscle is found in the sole of the foot. It is called _the short
flexor of the toes_. It arises from the calcaneum, and passes to the
four outer toes. In quadrupeds, it rises as high as the back of the
knee, and is found blended with the plantaris.
Further designated by the name of _the superficial flexor of the
phalanges_, covered in part by the gastrocnemius, with which it is in
relation for a great part of the course which it traverses, this muscle
arises from the posterior surface of the femur, on the external branch
of the inferior bifurcation of the linea aspera. In the horse, this
origin takes place in a depression situated above the external condyle,
in the supracondyloid fossa. Then it accompanies the gastrocnemius, and
becomes tendinous where the tendo-Achillis commences. It then winds
round the latter in placing itself on its inner side, then on its
posterior surface, and reaches the calcaneum. It accordingly
contributes, as we have already pointed out, to form the cord of the
ham. After having become expanded, and having covered as with a sort of
fibrous cap the bone of the heel, it descends behind the metatarsus, and
presents there an arrangement analogous to that which we pointed out in
connection with the superficial flexor of the digits--that is, it
contributes to form the _tendon_. This prominence, in the form of a
cord, we see behind the canon-bone in solipeds and ruminants. It
finally terminates in the same way as the muscle with which we have
compared it (see p. 197).
In the horse, its fleshy body is but slightly developed, so that its
tendon alone is specially visible in the superficial muscular layer, but
in the dog and the cat it is large. Hence it results that its fleshy
body appears on each side of the inferior half of the gastrocnemius, and
produces an elevation which recalls that which the soleus produces on
each side of the same muscles in the human species.
The muscles which follow form, with the popliteus, which we have already
studied, the deep layer of the posterior region of the leg.
=Flexor Longus Digitorum= (Fig. 87, 19; Fig. 88, 17).--This muscle, in
man, is the only common flexor of the toes belonging to the muscles of
the leg.
In comparison with the preceding muscle, it is a deep flexor.
Veterinarians have given it the name of _the oblique flexor of the
phalanges_.
Visible on the internal aspect of the superficial layer of the muscles
of the leg, this muscle arises above from the posterior surface of the
external tuberosity of the tibia, becomes tendinous, passes towards the
metatarsus, and blends with the tendons of the posterior tibial and the
long proper flexor of the great-toe. In the dog and the cat it is
blended with this latter only.
=Tibialis Posticus= (Fig. 85, 14; Fig. 86, 12; Fig. 87, 20; Fig. 88,
16).--This muscle arises from the external tuberosity of the tibia, and
from the head of the fibula. Thence it passes to the tarsus, and
terminates in different fashion in carnivora and other quadrupeds.
In the dog and the cat, it is inserted into the ligamentous apparatus of
the tarsus, or into the base of the second metatarsal.
In the other quadrupeds with which we are here occupied it is blended
with the long proper flexor of the great-toe.
It is accordingly in the carnivora that the mode of termination of the
tibialis posticus most nearly resembles that of this same muscle in the
human species. From this independence there results a special action.
It is an adductor and internal rotator of the foot.
=Flexor Longus Pollicis= (Fig. 84, 18; Fig. 85, 14; Fig. 86, 12; Fig.
87, 18; Fig. 88, 16).--This muscle, as that in man, is the most external
of the deep layer of the leg. It is on the external aspect of the latter
we perceive it, between the peroneals and the gastrocnemius or
tendo-Achillis.
It arises from the fibula and tibia, and is thence directed towards the
tarsus. It unites with the long common flexor of the toes to form with
it _the deep flexor of the phalanges_, of which it is the principal
fasciculus. We may add that in the dog and the cat the posterior tibial
remains independent of this latter, but that in the pig, ox, and horse
the posterior tibial is united to the preceding to form with them the
deep flexor muscle.
Thus constituted, the deep flexor goes towards the phalanges, where it
terminates as the deep flexor of the digits of the fore-limbs (see p.
197). In animals possessed of a canon it contributes to form the
_tendon_ (Fig. 85, 16; Fig. 86, 14, 14; Fig. 88, 19, 19).
Muscles of the Foot
We must remember that on the dorsal surface of the foot in man we find
but a single muscle--the dorsalis pedis. The remaining subcutaneous
structures of this region consist of the tendons of the anterior muscles
of the leg which occupy this dorsal aspect.
=Dorsalis Pedis= (Fig. 84, 19).--Also called the extensor brevis
digitorum, the dorsalis pedis muscle is found in all domestic
quadrupeds; but its development is so much the less as the number of
digits is more reduced.
In the dog and the cat it arises from the calcaneum, and is inserted
into the three internal toes (the first toe excepted) by uniting with
the corresponding tendons of the common extensor.
In the pig its disposition is analogous.
As for the dorsalis pedis of the ox and the horse, it is extremely
rudimentary, and occupies the superior part of the canon. It is a small,
fleshy body, situated on the anterior surface of the metatarsus, which
arises from the calcaneum, whence it passes to unite at its inferior
extremity with the tendon of the extensor of the phalanges.
As regards the muscles of the sole of the foot, we think it unnecessary
to occupy ourselves at any length with them because of their slight
importance with regard to external form.
We will only recall that in the median portion of this plantar surface
we find in man the short flexor of the toes, which in quadrupeds arises
higher up, from the posterior surface of the femur; that it belongs to
the muscles of the leg; and that it forms the superficial flexor of the
toes, which we have already studied.
We may further add that the suspensory ligament of the fetlock in
ruminants and solipeds represents, as in the fore-limbs, the
interosseous muscles.
MUSCLES OF THE HEAD
We will divide these muscles into two categories: masticatory and
cutaneous.
Masticatory Muscles
The muscles of this group which specially interest us are the masseter
and the temporal. As regards the pterygoids, since they are situated
within the borders of the inferior maxillary bone, and consequently do
not reach the surface, we shall not require to occupy ourselves with
them here.
=Masseter= (Fig. 89, 2; Fig. 90, 1; Figs. 91, 92).--For those who have
studied the masseter of man, it is not difficult to recognise that of
quadrupeds. Nevertheless, the particular aspect which it presents in
different species gives to its study a certain interest.
Arising from the zygomatic arch, and passing downwards and backwards, it
is inserted into the external surface of the ramus of the mandible and
into its angle.
Its posterior border is in relation with the parotid gland (Fig. 90, 14;
Figs. 91, 92), this gland being situated between the corresponding
border of the lower jaw bone and the transverse process of the atlas.
Such are the general characters; the following are the particular ones:
In the carnivora it is thick and convex. In the horse it is flat, but
more expanded; it forms the _flat of the cheek_. In the ox it is flat,
as in the latter; but, while being less thick, it is more prolonged in
the vertical direction.
The form of the osseous parts which give it origin is, besides, in
relation with these differences, and explains the peculiar characters
which the masseter presents.
[Illustration: FIG. 89.--MYOLOGY OF THE DOG: MASTICATORY MUSCLES (A
DEEPER DISSECTION THAN THAT SHOWN IN FIG. 90).
1, Zygomatic arch; 2, masseter; 3, temporal exposed by the suppression
of the auricular and occipital muscles and the pinna of the ear; 4,
auditory canal; 5, inferior maxillary bone; 6, digastric.]
Indeed, in the dog and the cat the zygomatic arch, strongly convex,
springs up in a marked manner from the plane of the lateral aspects of
the skull.
In the horse the same arch, less prominent externally, is prolonged by a
rectilinear crest on the superior maxillary bone, where it is continued
in forming the zygomatic or maxillary spine.
In the ox the same crest ascends a good way towards the inferior margin
of the orbit in a curved direction with the concavity inferior, to
redescend afterwards on the external surface of the superior maxilla.
The masseter is an elevator of the lower jaw. It acts, above all, as in
the human species, in the process of mastication.
=Temporal Muscle= (Fig. 89, 3).--The development of the temporal is in
proportion to the energy of the movements of elevation which the lower
jaw has to execute.
It arises from the temporal fossa, and is inserted into the coronoid
process of the inferior maxilla.
Its development, enormous in the carnivora, is such that the muscle
projects beyond its fossa. It is less voluminous in the horse, and still
less so in the ox. In the latter, indeed, the temporal fossa, although
deep, is of small extent (see Fig. 62, p. 119); the frontal bone being
large, it is found to be thrown back on the lateral walls of the
cranium, below the osseous processes which support the horns and
overhang the fossa in question, as well as the muscle which it contains.
It is covered by the auricular muscles, and by the base of the pinna of
the ear.
Like the masseter, the temporal is an elevator of the lower jaw.
Cutaneous Muscles of the Head
=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.
[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 alaeque 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] Edouard 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]
[34] H. Straus-Durckheim, 'Anatomie descriptive et comparative du
chat,' Paris, 1845, t. ii., p. 210.
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 constitute
the small zygomatic.
[Illustration: FIG. 91.--MYOLOGY OF THE OX: MUSCLES OF THE HEAD.
1, Masseter; 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-labial; 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-labial_, or again, the _proper
elevator of the upper lip_, this muscle arises from the external surface
of the superior maxillary bone, passes 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-labial_.
Arising from the frontal and nasal bones, it thence passes 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 pass 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 pass under the internal fasciculus; in the horse
the deep elevator passes under the two fasciculi, and the canine passes
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
analogous situation. It does not exist in the ox or in carnivora. The
transversus nasi is a dilator of the nostrils.
[Illustration: FIG. 92.--MYOLOGY OF THE HORSE: 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, 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-labialis; 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 passes 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,
passes 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 passes 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 constitutes 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-labial_, 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, passes 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 pass 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-labialis_ (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 analogy with those of the auricular region of man, it is
very difficult, because of their complexity, to trace this analogy 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.
The zygomatico-auricularis, which we look on as the homologue 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 principal 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 pass
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 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 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 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 pinnae of the ears, these being caused by the folding of the
integument, whilst the pinnae 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.
=Zygomatico-auricularis= (Fig. 90, 11).--Arises from the internal
surface of the great zygomatic, passes 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 antitragus
of the human ear. It is to this antitragus, 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 passes 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 principal 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.