Bovine Forelimb - Anatomy & Physiology

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Structures of the Proximal Forelimb and Shoulder

Scapula

• The ox possesses a small tuber scapular
• It has acromion present
• It has extensive scapular cartilage

Humerus

• The humerus is essentially the same conformation as that of the dog.

Radius and Ulna

• These are complete bones in the ox but are entirely fused
• There is a proximal and distal interosseous space which are the only two places where the shafts are seperated
• The ulna's proximal end is caudal to the radius and it's distal end forms the lateral styloid process, distal to the radius and articulating with the ulnar carpal bone.

Joints of the Proximal Forelimb

Shoulder Joint

• The joint capsule attaches a very short distance from the periphery of the articular surfaces.
• The intertubercular (bicipital) bursa lies between the humeral tubercles cushioning the bicipital tendon.
• The bursa and tendon are held in place by the transverse humeral retinaculum running between the greater and lesser tubercles of the humerus.

Elbow Joint

• The joint capsule attaches to the articular surface of the condyle, the periphery of the olecranon fossa and the articular cartilage of the trochlear notch of the ulna. It fuses with the collateral ligaments.
• Paired collateral ligaments attach the epicondyles to the tuberosities of the radius and ulna.

Structures of the Distal Forelimb

Carpal bones

Carpal bones comprise two rows:

• Proximally, (mediolaterally), radial, intermediate, ulnar and accessory bones
• Distally, 1st is missing, 2 and 3 are fused

Metacarpal bones

These are covered in detail in the bovine phalanges section.

Joints of the Distal Forelimb

Carpal Joint

The carpal joint is a compound joint composed of:

• The antebrachiocarpal joint between the radius/ulna and the proximal carpal bones
• The middle carpal joint between the two rows of carpal bones
• The carpometacarpal joint between the distal carpal bones and the proximal metacarpals

The joint is a synovial joint, comprised of a common outer fibrous capsule and three inner synovial pouches, one for each joint. Numerous ligaments add to the stability of the joint and ensure movement is largely limited to the sagittal plane, although no collateral ligaments exist in the dog between the radius and the proximal metacarpals. This allows a very small amount of rotation.

Metacarpal Joint

The metacarpal joint is defined by the presence of palmar sesamoids, which allow the flexor tendons to pass over the sharp change in angle presented by the joint. These are paired on each digit, with the exception of the first digit where it exists.

Muscles of the Forelimb

Extrinsic Musculature

These muscle are responsible for joining tht forelimb to the trunk, forming a synsarcosis rather than a conventional joint. Collectively, they act to transfer the weight of the body to the forelimbs as well as stabilize the scapula.

Trapezius: Accessory n.

• Origin: mid-dorsal raphe and supraspinous ligament
• Insertion: spine of the scapula
• Body: two parts, cervical and thoracic separated by aponeurosis
• Action: raises scapula against the trunk and swings cranially to advance the limb

Brachiocephalic m.: Accessory n.

• Two parts separated by the clavicle where it exists
• Origin: clavicle or vestigial fibrous intersection
• Insertion: several places on the head and neck
• Actions:
  • advances the limb and extends the shoulder joint when limb is in motion
  • draws head and neck ventrally when limb is fixed

Omotransversarius: Accessory n.

• Origin: transverse processes of the atlas
• Insertion: acromion and adjacent scapula
• Action: advancing the limb
• Innervation

Latissimus dorsi: local branch of brachial plexus

• The broadest muscle of the back
• Origin: thoracolumbar fascia
• Insertion: teres tuberosity of the humerus
• Actions: antagonist to the brachiocephalic m.
  • cranial fibers strap scapula to the chest
  • retracts free limb and flexes shoulder joint
  • draws trunk forward over the fixed limb

Pectoral mm.: brachial plexus

• Two superficial parts, cranial and caudal
  • Origin: cranial sternum
  • Insertion:
    • cranial (descending): crest of the humerus distal to the deltoid tuberosity
    • caudal (transverse): covers elbow joint to insert on the medial fascia of the forearm
  • Action: adduct the forelimb, assist in protraction and retraction
• One deep part (pectoralis profundus), with cranial and caudal parts
  • Origin: ventral sternum and adjacent cartilage
  • Insertions:
    • cranial (subclavius): supraspinatus m.
    • caudal (pectoralis ascendens): lesser tubercle of the humerus
  • Actions:
    • slinging trunk between forelimbs
    • may also retract free limbs
    • draw trunk forward when limb is fixed

Serratis ventralis: branch of brachial plexus

• Origin: C4 to 10th rib
• Insertion: medial scapula and scapular cartilage
• Action: supporting the weight of the trunk
  • reinforced by strong fascia
  • cervical portion can retract the limb
  • caudal portion can advance the limb

Rhomboids: brachial plexus, although in some species, dorsal spinal nerves can innervate

• Origin: median connective tissue from poll to withers, lying deep to the trapezius
• Insertion: dorsal border and adjacent scapula
• Action: retracting the limb, may also raise limb

Intrinsic Musculature

Muscles of the Shoulder

These muscles are grouped:

• Lateral:Supraspinatus and Infraspinatus, Suprascapular n. of the brachial plexus
  • Origin: the fossae of the scapula
  • Insertion: both tubercles of the humerus
  • Action: brace the shoulder
  • Clinical significance: bursa between the tendon of the infraspinatus and lateral tubercle of the humerus can be the site of inflammation
• Medial:
  • Supscapularis: Subscapular n. from the brachial plexus
    • Origin: Deep surface of the scapula
    • Insertion: medial tubercle of the humerus
    • Action: braces medial shoulder joint, potential adductor
  • Coracobrachialis: Musculocutaneous n. of the brachial plexus
    • Origin: medial supraglenoid tubercle
    • Insertion: proximal shaft of the humerus
    • Action: fixator
• Caudal (Flexors): Axillary n. of the brachial plexus
  • Deltoids
    • Origin: caudal border and spine of the scapula
      • One head in the horse and two in species with an acromion (site of second origin)
    • Insertion: deltoid tuberosity on the humerus
  • Teres Major
    • Origin: dorsal part of the caudal scapula
    • Insertion: teres tuberosity midway down humerus
  • Teres Minor
• There are no defined extensors of the shoulder. Those involved (brachiocephalic m., biceps brachii, supraspinatus, and ascending pectorals) have other, more primary roles.

Muscles of the Elbow

Extensors: Radial n. from the brachial plexus

• Triceps brachii: Three heads, four in the dog
  • Long head: caudal margin of the scapula
  • Lateral, medial, and accessory heads: shaft of the humerus
  • Insertion: olecranon, proteced by tricipital bursa against the bone and subcutaneous bursa against the skin
• Tensor fasciae antebrachii
  • Overlies triceps extending from scapula to olecranon
• Anconeus
  • Origin: distal humerus
  • Insertion: lateral olecranon

Flexors: Musculocutaneous n. from the brachial plexus

• Biceps brachii
  • Origin: supraglenoid tubercle of the scapula
  • Insertion: medial tuberosity of proximal radius and adjacent ulna
  • Runs through the intertubercular groove of the humerus
• Brachialis
  • Origin: proximocaudal humerus
  • Insertion: spirals to insert next to biceps

Muscles of Supination and Pronation

Supinators: Radial n. from the brachial plexus

• Brachioradialis
  • Origin: lateral epicondyle of the humerus
  • Insertion: distal medial forearm within superficial fascia
  • Prominent in the cat but nearly absent in the dog
• Supinator
  • Deep to extensor muscles, passing from lateral humeral epicondyles to upper medial radius

Pronators: Median n. from the brachial plexus

• Pronator teres: only functional in cat and dog
  • Origin: medial epicondyle of the humerus
  • Insertion: supinator
• Pronator quadratus: only found in carnivores
  • Origin: shaft of the ulna
  • Insertion: shaft of the radius

Muscles of the Carpal and Digital Joints

Extensors: Radial n. from the brachial plexus

• Craniolateral position on the forearm
• Almost all originate from the lateral epicondyle of the humerus
• Extensor carpi radialis: most medial, inserts on 2nd/3rd metacarpal bone
• Ulnaris lateralis: most lateral, inserts on accessory carpal bone
• Extensor carpi obliquus: aka abductor pollicis longus
  • Origin: cranial radius
  • Insertion: most medial metacarpal bone
• Last two may also serve in medial deviation of the paw
• Common Digital Extensor
  • Insertion: extensor process of the distal phalanx of each digit
  • Sends a medial branch to dewlcaw and medial digits in all but horse and cat
• Lateral Digital Extensor
  • Insertion: dorsal proximal phalanx

Flexors: Median or Ulnar n. of the brachial plexus

• Caudal position on the forearm
• Originate from the caaudal medial epicondyle of the humerus
• Flexor carpi radialis: most medial, inserts on upper 2nd/3rd metacarpal bone
• Flexor carpi ulnaris: most lateral, inserts on the accessory carpal bone
• Superficial Digital Flexor
  • Branches according to the number of digis and inserts in proximal interphalangeal joint
• Deep Digital Flexor
  • Passes through carpal canal before branching and continues to palmar distal phalanges

Interosseus muscles

• Support metacarpophalnageal joints
• Arise from palmar proximal metacarpal bones and insert on sesamoid bones within the joints, continued by ligaments to phalanges

Vasculature of the Forelimb

• Arteries of the Forelimb
• Veins of the Forelimb
• Lymphatics of the Forelimb