Muscles of the Thoracic Limb Lecture Notes

Overview

• Thoracic Limb Muscles are categorized into:
  • Intrinsic Muscles: Origin and insertion in one region (bones of thoracic limb).
  • Extrinsic Muscles: Span from one body region to another.
  • Joint-specific Grouping:
    • Shoulder girdle
    • Shoulder joint
    • Elbow
    • Carpus
    • Digits
  • Functional Subgroups:
    • Extensors
    • Flexors
    • Adductors
    • Abductors

Shoulder Girdle Muscles

• Trapezius Muscle: Flat, triangular; swings scapula forward/backward.
  • Cervical part (larger)
  • Thoracic part (smaller)
• Rhomboideus Muscle: Deep to trapezius, composed of three parts.
  • Rhomboideus capitis: Originates on occipital bone.
  • Rhomboideous cervices: Originates at cervical raphe.
  • Rhomboideous thoracis: Originates on thoracic vertebrae T4-T7.
• Serratus Ventralis: Largest muscle attaching thoracic limb to the trunk.
• Homo Transversarius: Pulls distal scapula forward; assists lateral neck flexion.

Shoulder Joint Muscles

Extensors

• Brachiocephalicus Muscle: Extends from head to arm; principal shoulder extensor.
  • Clidobrachialis
  • Clidosephalicus (Clidomastoidus & Clidoservicalis)
• Supraspinatus: Stabilizes shoulder joint.

Flexors

• Latissimus Dorsi: Strong shoulder flexor; pulls limb caudally or advances trunk.
• Deltoidius Muscle: Extends from scapula spine to humerus.
  • Scapular part
  • Acromial part
• Infraspinatus: Acts as collateral ligament; may abduct, flex, outwardly rotate shoulder.
• Teres Major & Minor: Strong shoulder flexors.

Adductors

• Pectoral Muscles: Strong forelimb adductors.
  • Superficial pectoral
  • Deep pectoral (advances trunk)
• Subscapularis: Stabilizes shoulder medially.
• Coracobrachialis: Extends shoulder despite location suggesting flexion.

Elbow Muscles

• Extensors: Stronger due to weight support.

  • Triceps Brachii: Main elbow extensor. Four heads in dogs (Long, Lateral, Medial, Accessory).
  • Anconius: Covers elbow joint capsule.
  • Tensor Fascia Antebrachii: Tenses antebrachial fascia; assists in elbow extension.

• Flexors:

  • Biceps Brachii: Chief elbow flexor.
  • Brachialis & Pronator Teres: Classified as flexors.

Carpus and Digits Muscles

Extensors

• Extensor Carpi Radialis: Largest carpus extensor.
• Common Digital Extensor: Longest thoracic limb extensor.
• Lateral Digital Extensor: Varies by digit presence.
• Extensor Carpi Ulnaris: Weak carpus flexor; outwardly rotates forearm.
• Extensor Carpi Obliquus (Abductor Pollicis Longus): Deep to digital extensors.

Flexors

• Flexor Carpi Radialis & Ulnaris: Carpus flexors; may slightly extend elbow.
• Digital Flexors:
  • Superficial Digital Flexor
  • Deep Digital Flexor: Only muscle to flex distal interphalangeal joint.

Conclusion

• Muscle actions are not exclusive to one joint.
• Proceed to Part 4: Muscles of the Pelvic Limb.