VAN 121: Veterinary Gross Anatomy-II (2+2)

LEG (POSTERIOR ASPECT)

Dissection  

•  Make an incision on the skin across the posterior aspect of the stifle and connect it to the vertical incision made on the medial and lateral aspect of the thigh.
• Make a vertical incision along the posterior medial line of the leg joining the previous incision to that round the hock. Reflect the two flaps of the skin to the sides.

Saphenous artery, nerve and vein

• These three structures from the medial aspect of the thigh descend down the medial aspect of the leg subcutaneously and reach the medial aspect of the hock.
• Saphenous artery on reaching the hock divides into lateral and medial tarsal arteries.
• The lateral tarsal artery is small supplies the tendoachilis and pierces the deep fascia and reaches the lateral aspect of the hock.
• The medial dorsal artery passes down in company with the tibial nerve along the deep flexor tendon and divides into medial and lateral plantar arteries, which accompany the plantar nerve dervied from the tibial nerve down the metatarsus.
• Saphenous vein is the upward continuation of the medial metatarsal vein.
• Saphenous nerve supplies all along its course fine branches to supply the skins on the medial aspect of the leg and finally it divides into anterior and posterior branches on the medial aspect of the hock.
• The terminal branches descend down the metatarsus and supply the skin on the medial and posterior aspects.

Dissection

• Cut the tendons of insertion of semitendinosus and semimembranosus and remove them.
• Now clean the gastrocenemius and its tendon.

Gastrocnemius

• It is a strong powerful muscle having two heads of origin.
• Medial head arises from the supracondyloid crest and the lateral head from the outer lip of the supracondyloid fossa of the femur.
• The two heads units to form a common belly, which is succeeded by a tendon about the middle of the leg.
• The tendon at first is superficial; it twists round the tendon of the superficial flexor laterally and lies anterior and deeper to its both the tendons together constituting the tendons together constituting the tendo Achilles.
• The tendon is finally inserted to the summit of the tuber calcis. Note the solelus blending with the lateral head.

Superficial flexor of the digit

• It arises from the bottom of the supracondyloid fossa and its belly is belended with lateral head of the gastrocnemius and is completely covered by it.
• It is succeeded by a tendon about the middle of the leg, which at first deep and then becomes superficial as the tendon of the gastrocenemius winds round it.
• At the hock, the tendon has a synovial sheath.
• It passes over the groove of the tubercalcis where it is inserted by two slips to the lateral aspects of the tubercalcis.
• It descends behind the tibial tarsal and passes down the metatarsus.

Dissection

• Cut the origin of the superficial flexor and reflect it down with the gastrocnemius.
• Clean the fascia and define the deeper layer of muscle and secure the branches of the tibial nerve and the posterior tibial artery supplying them.
• Clean the tendon of origin of the popliteus and while doing so, note its relation to the lateral meniscus and joint capsule of the femorotibial articulation.
• While cleaning the tendons of the deep flexor feel with fingers the synovia from their synovial sheaths.

Poplitieus

• It is a triangular muscle on the upper part of the posterior face of the tibia.
• It arises by a tendon from the lower depression on the lateral condyle of the femur and is suceeded by a triangular belly, which is attached to the popliteal line on the tibia.

Deep digital flexor

• It covers the rest of the posterior face of the tibia below popliteal line.
• It has three heads of origin viz. medial, superficial and deep.
• The superficial and deep heads arise from the lateral condyle, lateral border and the posterior face of the tibia below the popliteal line.
• The tendons of the superficial and deep heads unite above the hook and the common tendon enclosed in a synovial sheath passes down through the tarsal sheath and descends down the metatarsus.
• The tendon of the medial head provided with a synovial sheath passes under the medial ligament of the hock and joins the common tendon about the upper third of the metatarsus.

Tibial nerve

• It is the continuation of the sciatic nerve in the leg.
• It passes between the two heads of gastrocnemius, runs over the popliteus and deep flexor, emerges under medial head of the gastrocnemius and runs subcutaneously, in front of the tendo achilles on the medial aspect of the lower part of the leg and divides on reaching the hock into, lateral and medial plantar nerves.
• In its course, it supplies branches to the gastrocnemius, superficial flexor, popliteus and the deep flexor.

Popliteal artery

• It is the continuation of the femoral artery between the two heads of the gastrocnemius.
• It supplies branches to the gastrocnemius, superficial flexor and divides into anterior and posterior tibial arteries.
• The posterior tibial artery supplies the popliteus and deep flexor.
• The anterior tibial artery passes deeply on the posterior capsular ligaments of the stifle under the popliteus, turns outwards below the lateral condyle of the tibia under the origin of the lateral digital extensor and gains the later face of the tibia.

Dissection

• Cut the tendon of the origin of popliteus and reflect the muscle backwards to expose the anterior tibial artery.
• Cut the origin of the lateral digital extensor without injuring the artery passing under it.
• Reflect the muscle and secure the branches suplying it and note the anterior tibial artery winding round the lateral border of the tibia to gain its lateral face.