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

THIGH (MEDIAL ASPECT)

Dissection  

While separating the limbs an incision on the skin along the ventral median line of the body has been made. From this, make a vertical incision on the skin about the median line of the thigh and extend it a little below the condyle of the femur.

Reflect the two flaps of the skin to the sides exposing the medial aspect of the thigh. Clean the muscles, saphenous vessels and nerve.

Saphenous artery, vein and nerve

• These three structures emerge from the interstice between the sartorius and gracilis pass obliquely downwards and backwards subcutaneously on the medial aspect of the thigh and leg. The nerve is in front, the artery is in the middle, and the vein is behind.
• The nerve detaches fine branches in the thigh to supply skin on the medial aspect. The artery also supplies fine branches to the skin. Further details of these structures should be examined at a later stage.

Sartorius

• It is a narrow band like muscle extending from the iliac region to the stifle.
• It has two bands of origin-one arising from the iliac fascia and the other from the tendon of psoas minor and the shaft of the ilium.
• It is between these two heads, the femoral artery and the saphenous nerve enter to descend into the femoral canal.
• The muscle passes down infront of the gracilis and its aponeurotic tendon joins that of the gracilis to be inserted to the medial straight ligament of the patella.

Gracilis

• It is broad and quadrilateral covering the greatest part of the medial aspect of the thigh.
• It arises from the prepubic tendon and the pelvic symphysis where it is extensively blended with the fellow of the opposite side.
• Its aponeurotic tendon blends with that of the preceding to be inserted to the medial straight ligament of patella, medial face of the tibia and the fascia lata.

Dissection

• Cut the aponeurotic tendon of sartorius and gently reflect it upwards and note the branches of femoral artery and the saphenous nerve supplying it.
• The femoral canal is thus laid open in which the femoral artery, vein and the saphenous nerve are seen entering the anterior border of the gracilis.
• Reflect the sartorius to its origin and note a long branch of the saphenous nerve entering the pectineus.
• Vastus medialis: This is the medial head of the quadriceps muscle covering the shaft of the femur on its anterior and medial aspects. It arises from the medial face of the femur and is inserted to the medial patellar ligament.
• Femoral vein: It is the satellite of the femoral artery in the femoral canal. It receives the saphenous and the posterior femoral veins. It is continued above the femoral canal by the external iliac vein.
• Femoral artery: It is the continuation of the external iliac artery below the pubis into the femoral canal. It crosses the posterior face of the shaft of the femur obliquely from within outwards, leaving a vascular impression and dips in between the two heads of gastrocnemius to be continued as the popliteal artery.
• Note: The femoral artery detaches a number of collateral branches, anterior femoral artery, saphenous artery, posterior femoral artery and numerous muscular branches to supply sartorius, gracilis, vastus medialis and some branches to the stifle joint. Saphenous artery has been followed partly already. Excepting the posterior femoral artery, all other branches should be cleaned and secured.
• Anterior femoral artery: It is the first collateral branch arising from the femoral artery before it enters the femoral canal. It accompanies the femoral nerve and enters the quadriceps, which should be examined at a later stage.
• Saphenous artery: It arises from the medial face of the femoral artery about its middle in the femoral canal, emerges from the canal between the sartorius and gracilis with the saphenous nerve and the vein and passes subcutaneously on the medial aspect of the thigh and leg, which is to be examined later.

Dissection

• Cut the aponeurotic tendon of gracilis and also its origin from the ischial symphysis without injuring the saphenous structures and reflect the muscle forwards. While so doing secure on its deep face the long branch of the obturator nerve and the deep femoral artery supplying it.
• By reflecting the muscle forwards expose the posteiror face of the pectineus and secure the branches of the obturator nerve supplying it.
• Now gently press down the adductor placed behind the pectineus and secure the branches of the obturator nerve terminating in it.
• Now reflect the gracilis upwards to expose the pectineus completely.
• Pectineus: It is a small conical muscle lying behind vastus medialis covered completely by the gracilis. It arises from the prepubic tendon and the ventral face of the pubis and is inserted to the middle of the medial border of the femur about the nutrient foramen.
• Adductor: It is a thick conical muscle placed behind the pectineus covered completely by the gracilis. It arises from the ventral surface of the pubis and ischium and is inserted to the posterior face of the femur.
• Semimembranosus: It is a large quadrilateral muscle placed between the adductor in front and the semitendinosus behind. It arises from the ventral face of the ischium and tuber ischi and inserted to the medial epicondyle (a rounded prominence above the condyle) of the femur and medial condyle of the tibia.
• Deep femoral artery: It arises from the common trunk of the external iliac artery above the pubis. It passes backward deeply under the pubis and disappears between pectineus and iliopsoas. To follow the course and to secure the branches of the deep femoral artery supplying the muscles, the dissector should proceed carefully sectioning the muscles as detailed below.

Dissection

• Cut the origin of the pectineus from pubis and gently press it down with the finger to follow the deep femoral under the obturator externus.
• While so doing, secure the branches supplying the pectineus, obturator externus and the long branch to gracilis on its deep face.
• At this stage, note the insertion of iliopsoas to trochanter minor. Divide the adductor across its middle and reflect both parts apart and secure the branches supplying it and the branches passing under it to reach the semimembranosus.
• Similarly divide the semimembranosus across its middle and reflect the parts apart to secure the branches supplying it and the branches passing under it to supply the biceps femoris and the semitendinosus. It is important for the dissector to remember that no part of any muscle should be removed.
• The dissection of the deep femoral artery is rendered more difficult by the satellite vein, which at every stage covers the artery. The vein should be carefully cut and removed in small segments at different stages to follow the artery and its branches.
• Reflect the semimembranosus downwards and forwards and clean the femoral artery. Note how it crosses the femur obliquely through the insertion of adductor and passes between the two heads of gastrocnemius. Trace the origin of the posterior femoral artery.

Posterior femoral artery

• It is the last collateral branch of the femoral artery.
• It is very short and arises from the posterior face of the femoral artery just before or as the artery passes between the two heads of gastrocnemius.
• It divides into ascending descending branches.
• The ascending branch passes between the semimembranosus and the biceps femoris and supplies them.
• The descending branch passes down on the lateral head of the gastrocnemius to supply it and the popliteal lymph gland. Often, the two branches arise at the same point from the femoral or otherwise separately.