Artistic Anatomy of Animals Part 25

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.

[Ill.u.s.tration: 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 pa.s.ses 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 princ.i.p.al metatarsal.

These two parts form a ring through which the terminal tendon of the fleshy portion of the same muscle pa.s.ses.

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 pa.s.ses 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 pa.s.sing 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 princ.i.p.al metatarsal, the other into the second cuneiform bone.

[Ill.u.s.tration: 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 pa.s.sing 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 pa.s.sage 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 pa.s.s to the latter. Lastly, it has been considered as being the h.o.m.ologue 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.

[Ill.u.s.tration: 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 pa.s.sive fas.h.i.+on, 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 pa.s.ses, 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 s.p.a.ce 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 pa.s.ses 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 pa.s.s 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.

[Ill.u.s.tration: 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, princ.i.p.al 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, pa.s.ses in front of the tarsus, the princ.i.p.al 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 a.n.a.logous 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 pa.s.ses towards the tarsus and divides into two fasciculi, internal and external, which are continued by tendons. These pa.s.s 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.

[Ill.u.s.tration: 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.]

[Ill.u.s.tration: 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, princ.i.p.al 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 pa.s.s 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 const.i.tute 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.