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

Extensor muslce

EXTENSOR MUSCLE 

• These are situated around the dorsal and lateral aspects of the forearm. They are

Extensor carpi radialis Medial digital extensor Common digital extensor (Extensor digitalis communis) Lateral digital extensor (Extensor digitalis lateralis) Extensor carpi obliquus

Extensor carpi radialis

• This is the largest of the extensor muscles and lies over the dorsal face of radius in a nearly vertical direction extending from the lower end of the humerus to the upper end of the large metacarpal bone.
• Origin: A sharp ridge on the lateral epicondyle of the humerus and the rough pit outside the coronoid fossa.
  • The fleshy belly of the muscle becomes narrow below and succeeded by a thick tendon which passes down the middle groove on the distal end of the radius through a synovial sheath runs down over the dorsal capsular ligament of the carpus.
• Insertion: By a wide flat tendon to the metacarpal tuberosity. Its tendon is crossed over by the tendon of extensor carpi obliquus.
• Action: To extend the carpus, and flex the elbow.

Medial digital extensor

• The muscle is slender and situated lateral to the preceding.
• Origin: The lateral epicondyle of the humerus and the rough pit outside the coronoid fossa.
  • The muscular belly passes down the forearm by a long narrow tendon about the lower third of the forearm. It then passes through a synovial sheath in common with the tendon of the succeeding muscle in the lateral groove over the dorsal face of the distal extremity of the radius. It passes down the dorso-lateralaspect of the carpus, lying over the dorsal capsular ligament of the carpus and continues its course in the metacarpal region gradually inclining medially. The tendon gradually widens over the first phalanx, receives two slips from the suspensory ligament.
• Insertion: By two branches to second and third phalanges of the medial digit.
• Action: To extend the joints of the medial digit and to abduct the digit.

Common digital extensor (Extensor digitalis communis)

• This is a long, slender muscle situated lateral to the preceding. It has two heads of origin.
• Origin: Lateral epicondyle of the humerus and from ulna.
  • The two heads of the muscle fuse about the middle of the forearm and the single belly thus formed. This belly is succeeded by a tendon above the lower third of the forearm and runs in company of the tendon of the preceding muscle in a common synovial sheath in the lateral groove on the dorsal aspects of the distal extremity of the radius. It then runs down the dorsolateral aspect of the carpus over the dorsal capsular ligament of the carpus then down the metacarpus gradually inclining forwards. At the fetlock it divides into two branches.
• Insertion: Each branch of the tendon is inserted to the extensor process of the third phalanx.
• Action: To extend the joints from the carpus downwards and to approximate the digits.

Lateral digital extensor (Extensor digitalis lateralis)

• The muscle is situated lateral to the preceding.
• Origin: Lateral ligament of the elbow: lateral tuberosity of the radius, and the shafts of radius and ulna.
  • The muscle terminates in a tendon, a little above the carpus which passes through a synovial sheath on the lateral aspect of the carpus, passes down the metacarpal region behind the tendon of the preceding muscle, expands as it reaches the first phalanx and receives two slips from the suspensory ligament.
• Insertion: The second and third phalanges of the lateral digit.
• Action: To extend the joints of the lateral digit and to abduct them.

Extensor carpi obliquus

• The muscle extends from about the middle of the lateral aspect of the forearm in an oblique direction downwards, forwards and inwards to the medial aspect of the upper part of the metacarpal region.
• Origin: Lateral and dorsal faces of the radius and ulna.
• The muscle lies under the preceding muscles. The origin is wide and the muscle is succeeded by a flat tendon at the lower third of the forearm, crosses over the tendon of the extensor carpi radialis obliquely inwards, and passes through a synovial sheath in the medial groove on the dorso-medial aspect of the radius.
• Insertion: A tubercle on the postero-medial aspect of the upper extremity of the large metacarpal bone.
• Action: To extent the carpus and rotate it outwards.
• Blood supply to all extensors: Collateral radial artery.
• Nerve supply: Radial nerve.