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

SUPRASCAPULAR REGION - LATERAL ASPECT

• Now the body should be suspended from the sling in the natural position to dissect the lateral aspect of the shoulder.

Dissection

• Make a longitudinal incisioin along the dorsal median line extending from the occipital region to the lumbar region.
• A vertical incision along the long axis of scapula from the region of the hump to a little below the shoulder joint is made and the two flaps of the skin are reflected aside. While reflecting the skin, note the series of cutaneous nerves arising lateral to the middorsal line.
• While reflecting the flaps of the skin care should be taken to retain the cutaneous muscle of the shoulder, which is band like.
• Reflection of the posterior flap of the skin over the trunk should be carefully done to retain the cutaneous muscles of the trunk in its lower part.
  • Trapezius
    • It is a thin wide triangular muscle extending from the dorsal median line over the scapula.
    • The fibres of its cervical part are directed downwards and backwards, whereas those of the dorsal part are directed downwards and forwards.
    • Clean the anterior (Ventral) border of trapezius, which is in apposition with the posterior (dorsal) border of brachiocephalilcus, by first noting the exit from under the brachiocephalicus and the course of the dorsal branch of spinal accessory nerve on the deep face of the muscle.
    • It covers the scapular muscles.

Dissection

• Cut the trapezius close to its insertion and reflect it upwards.
• While reflecting the cervical part, note the dorsal branch of the spinal accessory nerve entering its deep face to supply it and also note a mass of fat with a chain of haemolymph glands.
• Now clean the rhomboideus and latissimus dorsi.
  • Spinal accessory nerve
    • This is the eleventh cranial nerve passing between the brachiocephalicus and oma-transversarius, the dorsal branch of which is seen terminating in trapezius.
  • Rhomboideus
    • Its cervical part is narrow and triangular and the dorsal part is quadrilateral. It is inserted to medial face of the scapular cartilage.
  • Nerves to Rhomboideus
    • Dorsal primary branches of fifth, sixth and seventh cervical spinal nerves after passing through the serratus cervicis, enter its lower border and terminate in it.
    • These nerves should be secured by a careful search in the fascia below the lower border of the muscle.
  • Latissimus dorsi
    • It is an extensive thin muscle extending from the lumbodorsal spine to the medial aspect of the arm.
    • It has an aponeurotic tendon arising from the lumbar and dorsal spines.
    • Its muscular part begins at a curved line corresponding to the twelfth rib and passes to the medical face of the humerus for insertion.
    • At the dorsal angle of the scapula, the muscular part detaches a narrow bundle, tensor fasciae antibrachii, which passes along the posterior border of the long head of triceps to the inserted to the olecranon.
    • Insertion of the mucle should be examined only after the limb is detached from the body.

Dissection

• Cut the muscular part of latissimus dorsi along its origin reflect it over the scapula.
• Reflect the cutaneous muscle of the trunk downwards and secure the external thoracic nerve on its deep face.
• Cut the insertion of serratus thoracis.
  • External thoracic nerve
    • The origin and the course of the nerve can now be examined by opening the axilla from behind.
    • The nerve arises from the posterior part of the brachial plexus and passes backwards in the axilla on the deep face of the deep pectoral to supply the cutaneous muscle of the trunk.
  • Brachiocephalicus
    • Most of this mucle belongs to the neck.
    • The dissector of the forelimb should examine only that part in front of the shoulder and its insertion to the crest of the humerus.
  • Oma-transversarius
    • This muscle belongs to the neck and is mostly under the preceding muscle.
    • Only its terminal part in front of the shoulder is inserted to the scapular fascia.

Dissection

• Extend the intial incision made on the scapular region and connect it to the incision made on the median pectoral groove.
• Now cut the lower parts of the brachiocephalicus and omotransversarius in front of the shoulder joint.
• Abduct the limb, open the axilla and cut the brachial plexus carefully leaving the roots of the plexus for later examination.
• Cut the insertion of the serratus cervicis and thoracis and rhomboideus.
• Now the forelimb is removed from the trunk and laid on the table.
• Now examine on the body, the roots of the brachial plexus without much disturbance to the scalenus, which should be left to the dissector of the neck.
  • Brachial Plexus
    • This is flat bundle of nerves appearing between the scalenus dorsalis and ventralis.
    • The roots emerge between the two divisions of the scalenus.
    • The branch from the sixth and seventh are directed backward.
    • The branch from the eighth cervical and first dorsal is directed forward.
    • The slender branch from the second dorsal unites with the first dorsal medial to the first rib and so cannot be seen at this stage.
    • The branches from the plexus can be traced on the limb.