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

ARM - MEDIAL ASPECT

Dissection

• Remove the pectorals by cutting close to their insertion.
• Now the brachial region is exposed with the several blood vessels and nerves overlying the muscles.
• The dissector should carefully clean and defind the muscles without injuring other structures that are overlying them.
• First he should note the relative positions of the nerve and blood vessels.
  • Brachial Artery
    • It passes down nearly vertically on the medical face of the humerus overlying the coracobranchials, gains the medial aspect of the elbow and disappears under the pronator teres to be continued as the median artery in the forearm.
    • The brachial vein, placed behind, accompanies it.
  • Coracobrachialis
    • It is small muscle lying on the medial face of arm.
    • Its tendon of origin from the coracoid process of the scapula crosses over the tendon of insertion of subscapularis.
    • It belly has two parts between which musculocutaneous nerve and the anterior circumflex artery pass to terminate in the biceps brachii.
  • Biceps brachii
    • It is a large powerful muscle partly on the medial face but mostly on the anterior face of the arm.
    • Its strong tendon or origin arises from the tuber scapulae and passes through the bicipital groove between two tendons of supraspinatus.

Dissection

• Cut the insertion of the superficial part of the coracobrachialis and raise it gently upwards without injuring the nerve and vessels passing under it.
  • Anterior circumflex artery
    • It is small artery arising from the anterior face of the brachial artery.
    • It passes in company with the musculocutaneous nerve between the two parts of coracobrachialis, supplying it and terminates in the upper part of biceps brachii.

Dissection

• Clean the triceps carefully without injuring blood vessels and nerves entering it.
  • Triceps
    • It is a large mucle filling the triangular space behind the shoulder joint between the scapular above, humerus in front and the olecranon behind.
    • It has three-heads - long head, medial head and lateral head-now, only the long and medial heads are visible.
  • Long head
    • It is large triangular muscle arising from the posterior border of the scapula and is inserted by a strong tendon to the olecranon, it has along its posterior border tensor fasciae antibrachii blended with it.
  • Medial head
    • This is the smallest head situated on the medial face of the humerus.
  • Deep brachial artery
    • It is a small artery arising from the posterior face of the brachial artery.
    • It divides into branches, which supply the triceps brachii, and passes deeply to olecranon fossa to supply anconeus, which has to be examined later.

Dissection

• Cut the origin of long head from the scapula and gently reflect it downward without injuring the nerves and blood vessels passing behind the shoulder joint and note radial nerve, deep brachial artery entering the muscle.
  • Posterior circumflex artery
    • This artery arises from the subscapular artery and passes behind the shoulder joint accompanied by the axillary nerve.
    • It divides into superior and inferior branches. The superior branch, with the nerve passes outwards to the deep face of the deltoideus, which should be examined later.
    • The inferior branch passes down between the divisions of the triceps and branches to all three heads, anconeus and passes down over brachialis.
  • Radial nerve
    • It is the largest nerve arising from the posterior part of the brachial plexus.
    • It is placed behind the ulnar nerve covered by the brachial artery and vein. About the middle of the arm, it leaves the company of vessels, passes back and disappears between divisioins of triceps supplying branches to all the three heads and anconeus.
    • Its further course should be examined later.
  • Ulnar nerve
    • It arises from the brachial plexus, passes down the medial aspect of the arm covered by the brachial artery, then it leaves the company of the artery, passes backward under the brachial vein, reaches the medial aspect of the elbow accompanied by the collateral ulnar artery, detaches a long cutaneous branch, which passes down the olecranon to supply the skin, on the volar aspect of the forearm.
    • The ulnar nerve with the collateral ulnar artery disappears between the two heads of flexor carpi ulnaris is which should be examined later.
  • Collateral ulnar artery
    • It is a small artery arising from the posterior face of the brachial artery above the elbow passes under the brachial vein obliquely downward and backward over the medial face of the elbow and accompanies the ulnar nerve between the two heads of flexor carpi ulnaris.
    • [Note: in most specimens two branches, which run one below the other, represent the collateral ulnar artery]
  • Median nerve
    • It is a very large nerve arising from the brachial plexus. A short branch of the musculocutaneous nerve to form the loop through which the brachial artery passes joins it.
    • It passes in front of the brachial artery, gains the medical aspect of the elbow where it disappears under pronator teres accompanied by median artery. About the middle of the arm it detaches a musculocutaneous branch, which passes outwards between coracobrachialis and biceps brahii.

Dissection

• Cut the belly of biceps at its middle and reflect the lower part down and follow the musculocutaneous branch of median nerve.
• The nerve reaches the lower part of brachialis, supplies a muscular branch, which enters the deep face of the muscle and is then continued down at the cutaneous branch to supply the skin in front and the medial aspect of the forearm, which should be examined later.
• Now cut the tendon of long head to triceps from the medial aspect of the olecranon and raise it upwards which exposes anconeus occupying the olecranon fossa.
  • Anconeus
    • It is a small muscle occupying the olecranon fossa attached to its margins.
    • Clean the muscle and note the branches of radial nerve, deep brachial artery and the inferior branch of the posterior circumflex artery supplying it.
  • Collateral radial artery
    • This is the last collateral branch of brachial artery from its lateral face.
    • It passes outward behind the lower part of biceps passes across over the capsule of the elbow joint and disappears under the origin of the extensors of the carpus and digit.
    • It should be examined later.