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 an acromion present and 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 separated. The ulna's proximal end is caudal to the radius and its 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

The carpal bones comprise two rows:

Proximally (mediolaterally), radial, intermediate, ulnar and accessory bones.

Distally, 1st is missing, 2 and 3 are fused and there is also a 4th carpal bone.

Metacarpal bones

These are covered in detail in the bovine lower limb section.

Joints of the Distal Forelimb

Carpal Joint

The carpal joint is a compound joint composed of:

1. The antebrachiocarpal joint between the radius/ulna and the proximal carpal bones.

2. The middle carpal joint between the two rows of carpal bones.

3. The carpometacarpal joint between the distal carpal bones and the proximal metacarpals.

The joint is a synovial joint, consisting 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 the 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:

Innervated by: 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.:

Innervated by: Accessory n.
The two parts are separated by the clavicle, where it exists.
Origin: occipital bone, nuchal ligament and the mastoid process.
Insertion: deltoid tuberosity and fascia of the limb.
Actions: advances the limb and extends the shoulder joint when limb is in motion. Draws the head and neck ventrally when the limb is fixed.

Omotransversarius:

Innervated by: Accessory n.
Origin: transverse processes of the atlas.
Insertion: acromion and spine of scapula.
Action: advancing the limb.

Latissimus dorsi:

Innervated by: 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. The cranial fibers strap the scapula to the chest. It retracts the free limb and flexes shoulder joint. It draws the trunk forward over the fixed limb.

Pectoral mm.:

Innervated by: brachial plexus
Two superficial parts, cranial and caudal, these aren't very distinct in the ox.
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 and assist in protraction and retraction.

Serratis ventralis:

Innervated by: branch of the brachial plexus.
Origin: C4 to 10th rib.
Insertion: medial scapula and scapular cartilage.
Action: supporting the weight of the trunk. It is reinforced by strong fascia. The cervical portion can retract the limb and the caudal portion can advance the limb.

Rhomboids:

Innervated by: brachial plexus
Origin: nuchal ligament.
Insertion: dorsal border and adjacent scapula.
Action: retracting the limb, may also raise the limb.

Intrinsic Musculature

Muscles of the Shoulder

These muscles are grouped:

1. Lateral

Supraspinatus and Infraspinatus:

Innervated by: 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.

2. Medial

Supscapularis:

Innervated by: 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:

Innervated by: Musculocutaneous n. of the brachial plexus.
Origin: medial supraglenoid tubercle.
Insertion: proximal shaft of the humerus.
Action: fixator.

3. Caudal (Flexors)

Deltoids:

Innervated by: Axillary n. of the brachial plexus.
Origin: Two heads of origin; the caudal border and spine of the scapula and the acromion.
Insertion: deltoid tuberosity on the humerus.
Action: Flexor of Shoulder.

Teres Major:

Innervated by: Axillary n. of the brachial plexus.
Origin: dorsal part of the caudal scapula.
Insertion: teres tuberosity midway down humerus.

Teres Minor:

Innervated by: Axillary n. of the brachial plexus.


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

Triceps brachii:

Innervated by: Radial n. from the brachial plexus
Has three heads, the medial branch is the most developed. The long head is at the caudal margin of the scapula; The lateral, medial, and accessory heads are at the shaft of the humerus.
Insertion: olecranon, proteced by tricipital bursa against the bone and subcutaneous bursa against the skin.

Tensor fasciae antebrachii:

Innervated by: Radial n. from the brachial plexus.
Overlies the triceps extending from the scapula to the olecranon.

Flexors

Biceps brachii:

Innervated by:Musculocutaneous n. from the brachial plexus.
Origin: supraglenoid tubercle of the scapula.
Insertion: medial tuberosity of proximal radius and adjacent ulna. It runs through the intertubercular groove of the humerus.

Brachialis:

Innervated by: Musculocutaneous n. from the brachial plexus.
Origin: proximocaudal humerus.
Insertion: spirals to insert next to biceps.

Muscles of the Carpal and Digital Joints

Extensors

All have innervation from the radial n. from the brachial plexus. They have a craniolateral position on the forearm and almost all of them originate from the lateral epicondyle of the humerus.

Extensor carpi radialis

The most medial, inserts on 2nd/3rd metacarpal bone.

Ulnaris lateralis

The most lateral, inserts on accessory carpal bone.

Extensor carpi obliquus (aka- abductor pollicis longus)

Origin: cranial radius.
Insertion: most medial metacarpal bone .

Common Digital Extensor

Insertion: extensor process of the distal phalanx of each digit.

Lateral Digital Extensor

Insertion: dorsal proximal phalanges.

Medial Digital Extensor

Insertion: middle and distal phalanges.

Flexors

All innervated by the median or ulnar n. of the brachial plexus. Have a caudal position on the forearm and originate from the caudal medial epicondyle of the humerus.

Flexor carpi radialis

The most medial, inserts on upper 2nd/3rd metacarpal bone.

Flexor carpi ulnaris

The most lateral, inserts on the accessory carpal bone.

Superficial Digital Flexor

Insertion: palmar surface of middle phalanges.

Deep Digital Flexor

Passes through carpal canal before branching and continues to palmar distal phalanges.

Interosseus muscles

This is covered in more detail in the bovine lower limb section.

Vasculature of the Forelimb

Click here for information on:

Arteries of the Forelimb

Veins of the Forelimb

Lymphatics of the Forelimb



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