Artistic Anatomy of Animals Part 24

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 s.p.a.ce.

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 h.o.m.ology 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 pa.s.ses 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 a.s.sociated 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 a.s.sists 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 const.i.tuted 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 _b.u.t.tock_, 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 a.n.a.l 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 ma.s.s 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 b.u.t.tock_. 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 a.n.a.l orifice, the resemblance to a small 'b.u.t.tock' is still more marked.

In lean horses a deep groove separates the ma.s.s 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 b.u.t.tock_, 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 s.p.a.ce 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 pa.s.s 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 const.i.tute 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 h.o.m.ologue of the anterior border of the human iliac bone).

The two fasciculi then pa.s.s 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 pa.s.ses 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