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

THIGH (LATERAL ASPECT)

Dissection  

• Extend the vertical incision through the skin made in the previous dissection down the thigh up to the upper third of the leg. Reflect the flaps of the skin on the side.
• Cutaneous nerves of the thigh: The cutaneous nerves of the hip descend in the superficial fascia and supply the skin on the lateral aspect of the thigh.
• Lateral cutaneous nerve on the leg: It arises from the sciatic nerve on the deep face of the biceps femoris pierces the lower part of the muscle and supplies the skin of the lower part of the lateral aspect of the thigh and the upper part of the leg.

Dissection

• Clean the superficial fascia and define the muscles.

Tensor fasciae latae

• Origin of the muscle from the lateral angle of the ilium has already been examined.
• The body of the muscle is elongated and placed along the anterior border of thigh, in front of the quadriceps.
• It is inserted to the fascia lata (deep fascia of the thigh and leg).
• On the deep face of the muscle, note the inferior branch of the circumflex iliac artery and the lateral cutaneous nerve of the thigh (from III lumbar nerve) supplying the skin on the medial aspect of thigh and the prefemoral lymph gland placed above the patella.

Biceps femoris

• The upper part of the muscle and its origin has already been examined.
• The lower part of the muscle extends on the posterior part of thigh covering the quadriceps partly and extends to the upper third of the leg.
• The muscle shows a deep vertical groove in its lower part through which the lateral cutaneous nerve of the leg pierces the muscle to supply the skin.
• The anterior concave border of the muscle overlaps the quadriceps.
• Along the posterior border the semitendinosus extends. Inferiorly, the belly of the muscle divides into two parts, which are succeeded by an aponeurotic tendon.
• The anterior part of this tendon is inserted to the patella, the middle part to the tibial crest and the posterior part to the tuber calcis.

Semitendinosus

• It is a long rounded muscle along the posterior border of the thigh placed between the semimembranosus medially and the biceps femoris laterally.
• It arises from the ventral face of tuber ischii passes along the posterior border of the thigh behind the biceps femoris, and lower down it turns medially and is succeeded by an aponeurotic tendon which is inserted to the medial face of tibial crest and the tuber calcis.

Dissection

• Cut the biceps femoris across about its lower third and reflect the muscle from before backwards to open the muscular canal through which the sciatic nerve descends in the thigh. Clean the fascia round the sciatic nerve and the several branches arising from it.
• Follow the muscular branches from the sciatic terminating in the biceps femoris, semimembranosus and semitendinosus.

Sciatic nerve

• From the hip, it passes between the great trochanter and tuber ischii, descends down the thigh behind the femur in the muscular canal formed by the biceps femoris and semitendinosus laterally and the semimembranosus and adductor medially.
• It passes between the two heads of the gastrocnemius and is continued down the leg as the tibial nerve.
• Its muscular branches to the biceps femoris, semitendinosus, and semimembranosus have already been cleaned.
• The origin of the lateral cutaneous nerve of the leg, which pierces the lower part of the biceps femoris and supplies the skin on the lateral aspects of the stifle, can be seen now as also the origin of the posterior cutaneous nerve of the leg and peroneal nerve.
• The former runs down on the lateral head of the gastrocnemius covered by the posterior tendon of the biceps femoris and reaches the lateral aspect of the leg.
• The latter runs down the stifle in front of the former covered by the middle tendon of the biceps femoris and reaches the muscles on the dorso lateral aspect of the leg. The course of both the nerves should be examined at a later stage.

Dissection

• Cut close to the origin of semimembranosus and reflect it down as also the adductor exposing the muscles on the ventral aspect of the pubis and ischium. Clean the fascia around the sciatic nerve and muscles between the tuber ischii and great trochanter.
• Secure a branch arising from the deep face of the posterior border of the sciatic nerve here and trace it into the gemellus and then throught it into the quadratus femoris.
• Gemellus: It is a small muscle placed behind and below the posterior border of the deep gluteus. It arises from the lateral border of the ischium at the lesser sciatic foramen and is inserted to the trochanteric fossa.
• Quadratus femoris: This is a small muscle, arises from the ventral face of the ischium and is inserted to the medial trochanter of the femur.
• Obturator externus: It arises from the ventral face of the pubis and ischium round the obturator foramen and is inserted with the tendon of the obturator internous to the trochanteric fossa.