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

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.

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

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.

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

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.

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.

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.