Cat shank and foot
Photo and text: Kyungmin Shin
Lateral view of the right shank and foot; the pes is to the right of the photo, while the knee is being held.
Deep medial view of the right shank and foot; gastrocnemius is reflected; pes is to the left of the photo.
A cat has only a limited range of motion at the foot joint, unlike arboreal animals or small animals. A cat can plantarflex and dorsiflex its foot, but it cannot invert or evert its foot. In its natural position, its toes are extended at the metartarsal-phalangeal joint and flexed at the proximal interphalangeal joints. Thus it walks on its pads, with its claws retracted. The anterior compartment of the shank and the foot consist mostly of tough tendinous muscles and tendons. In contrast, the posterior compartment of the shank and the foot is mostly consisted of fleshy muscles and some tendons. Overall, the posterior compartnment is a lot less tendinous than the anterior compartment. In contrast to the fox, the cat has muscle fibers running almost all the way down to the calcaneal tuber; the fox has relatively longer tendons in the posterior compartment.
| Muscle | Origin | Insertion | Action |
| Extensors | |||
| Tibialis anterior | Tibia, fibula and interosseus membrane | First metatarsal | Dorsiflexion of the foot |
| Extensor digitorum longus | Lateral epicondyle of femur | Bases of second phalanges on dorsal side of the foot | Extends phalanges |
| Extensor digitorum brevis | Distal border of the calcaneal ligament and dorsal surfaces of the three lateral metatarsals | Cartilaginous plate (sesamoid bones) that lies in the metatarsophalangeal joint of the digits on the outer side | Extends the digits |
| Peroneus tertius | Lateral surface of the fibula | Lateral border of the extensor tendon of the fifth digit between the first and the second phalanges | Dorsiflexion of the foot |
| Flexors | |||
| Peroneus brevis | Lateral surface of the fibula | Base of the lateral surface of the fifth metatarsal | Plantarflexion of the foot |
| Gastrocnemius | Lateral head-patella, femur, lateral sesamoid and fasciaMedial head-femur and lateral sesamoid | Calcaneus by tendo calcaneus | Plantarflexion of the foot |
| Plantaris | Lateral border of the patella, the lateral sesamoid and the femur | Calcaneus by tendon sheathed by the tendo calcaneus | Plantarflexion of the foot |
| Soleus | Lateral head and border of the fibula | Calcaneus | Plantarflexion of the foot |
| Peroneus Longus | Lateral surface of the fibula | Bases of the metatarsals | Plantarflexion of the foot |
| Tibialis posterior | Fibula and tibia | Navicular and intermediate cuneiform | Plantarflexion of the foot |
| Flexor digitorum longus | Tibia and fibula | Distal phalanges of the four digits | Flexes the toes |
| Flexor digitorum brevis (superficialis) | Continuation of the plantaris tendon | Distal metatarsals of the four digits | Flexes the toes |
| Flexor hallucis longus | Tibia, fibula, interosseus membrane and nearby muscles | Bases of the distal phalanx of the big toe | Flexes the toes |
| Popliteus | Lateral epicondyle of the femur | Tibia | Medial rotation of the tibia |
The hind leg and the foot are serially homologous to the forelimb and hand.
One of the major differences between the forelimb and the hind limb is their
range of motion: the forelimb has a larger range of motion. However, the hind
limb musculature is more massive than that of the forelimb.
The skin comes off easily for this part of the lab, but there are several tough
fascia and retinacula that are difficult to remove. When the skin is removed,
the musculature on the lateral side is visible, but the musculature on the medial
side is covered by the crural fascia and by the fascia covering the tibialis
anterior. From the lateral side of the body, the large muscle visible on the
caudal side of the shank is the lateral head of the gastrocnemius muscle. After
one removes the crural fascia, which covers from the medial head, the entire
gastrocnemius muscle is visible. This muscle is the largest muscle on the shank.
Cutting the gastrocnemius muscle near the tendo calcaneus and reflecting it
back, exposes the plantaris muscle, which is deep to the gastrocnemius muscle.
The plantaris muscle is separable from the lateral head of the gastrocnemius
muscle, but on the medial head, it seems to insert into the gastrocnemius muscle
and fuse with it. The soleus muscle lies deep to the plantaris. It also inserts
on the calcaneal tuber via the tendo calcaneus. These muscles are significant
flexors of the ankle.
On the lateral side of the shank, deep to the soleus muscle, lies the fibularis
brevis muscle. The fibularis tertius is deep to the fibularis brevis, while
the fibularis longus is cranial to the fibularis brevis muscle. These peroneus
muscles are fixed between the lateral side of the calcaneus and the tibia by
tough retinacula. The fibularis longus is held to the lateral side of the joint
by the extensor retinaculim. The fibularis tertius and fibularis brevis run
postrior to the lateral malleolus and then turn deep to the tendon of the fibularis
longus, which is what holds them in place. The peroneus tertius has longer tendons
than the brevis and extends all the way to the proximal phalanges, while the
peroneus brevis muscle inserts onto the lateral side of the fifth metatarsal.
Their tendons both run lateral to the extensor digitorum brevis muscle.
The extensor digitorum brevis muscle is the largest muscle on the dorsum of
the foot, and it is mostly tendinous. This muscle is deep to the tendons of
the extensor digitorum longus muscle. The extensor digitorum longus, unlike
the extensor digitorum brevis, originates from the femur, and becomes four tendons
before it reaches the foot. Medial and superficial to the extensor digitorum
longus muscle lies the tibialis anterior muscle. The tendon of the tibialis
anterior crosses the anke and inserts in the first metatarsal. A tough fascia
covers this muscle.
On the medial side of the hind limb, the flexor hallucis longus muscle is deep to the soleus muscle and overlies the flexor digitorum longus muscle. The tibialis posterior muscle is the deepest muscle lying against the posterior surface of the tibia. The popliteus muscle is superficial to the superior half of this muscle, its fibers running almost perpendicular to the tibialis posterior muscle, so that it acts as a rotator at the knee. However rotation at the knee is very limited in motion and though some very minimal amount of rotation might be possible when the knee is flexed. The flexor digitorum longus muscle is deep to the flexor digitorum brevis muscle, the reverse of the relationship of the pedal extensors. Overall, on the ventral side of the foot, there is more muscle fiber than tendon, whereas the dorsal extensors are more tendinous.