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.

Collateral ligaments extend from the radius to the metacarpal bones on the medial and lateral aspect of the carpus.
The carpal canal houses both the deep digital flexor tendon and the deep branch of the superficial digital flexor.

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