Anatomy of the Thoracic Limb Chapter 6

Study Notes

Extrinsic Muscles of the Thoracic Limb

Connect front limb to the body, positioned lateral and medial to the scapula.
No bony structure links front limb to the torso, relying on muscle attachments.
Caudal muscles retract the limb, while cranial muscles protract it.
M. latissimus dorsi: Originates from thoracic/lumbar vertebrae, inserts on medial brachium, innervated by thoracodorsalis nerve.M. trapezius
- Comprised of cervical and thoracic parts.
- Originates from spinous processes of cervical and thoracic vertebrae.
- Inserts onto the spine of the scapula.
M. omotransversarius
- Originates at the distal part of the scapular spine.
- Inserts on the wing of the atlas.
- Note: Diverges from M. trapezius, creating a triangular area without muscle.
M. brachiocephalicus
- Originates from the median raphe of the neck and mastoid process of the temporal bone.
- Inserts on the distal part of the humerus.
- Contains a fibrous intersection (clavicular intersection) affected by other muscle components.
M. rhomboideus
- Has capital, cervical, and thoracic parts.
- Originates from spinous processes of cervical and thoracic vertebrae and the back of the head.
- Inserts on the medial surface of the proximal scapula.
M. pectoralis superficialis
- Originates from the manubrium of the sternum.
- Inserts on the humerus.
M. pectoralis profundus
- Originates from the caudal aspect of the sternum.
- Inserts on the major and minor tubercles of the humerus.
- Innervated by the pectoral nerves.
M. serratus ventralis
- Composed of cervical and thoracic parts forming a sling to suspend the trunk.
- Originates from the medial aspect of the scapula.
- Inserts on the ribs and transverse processes of cervical vertebrae.
- Innervated by the long thoracic nerve.

Nerves of the Thoracic Limb

Brachial plexus formed from ventral rami of C6-T2.
Nn. pectorales innervate M. pectorales.
N. thoracicus longus innervates M. serratus ventralis.
N. axillaris serves true flexors of the shoulder joint.
N. thoracicus dorsalis innervates M. latissimus dorsi.
N. thoracicus lateralis supplies cutaneous muscles of the trunk.
N. subscapularis innervates M. subscapularis.
N. suprascapularis innervates M. supraspinatus and M. infraspinatus.
N. radialis: Extensors of the elbow, carpus, and sensory to cranial antebrachium and dorsal manus.
N. ulnaris: Flexors of the elbow, carpus, and sensory to caudal antebrachium and palmar manus.
N. medianus: Similar function as N. ulnaris; connects median nerve and musculocutaneous nerve.
N. musculocutaneous: Flexor muscles of the elbow and sensory to the medial antebrachium.

Blood Supply to the Thoracic Limb

Main arteries: Subclavian, Axillary, Brachial, and Median arteries provide blood to the thoracic limb.
Cephalic vein: Major vein draining the thoracic limb.

Muscles of the Shoulder Joint

Muscles arranged around the shoulder joint to facilitate flexion and extension.
Originates from the scapula and inserts on the humerus.
M. subscapularis
- Fills the subscapular fossa.
- Inserts on the minor tubercle of the humerus and acts as a medial collateral ligament.
- Innervated by the subscapular nerve.
M. teres major
- Originates from the caudal angle of the scapula.
- Inserts on the medial, proximal end of the humerus.
- Responsible for shoulder flexion and innervated by the axillary nerve.
M. supraspinatus
- Originates from the supraspinous fossa of the scapula.
- Inserts on the major tubercle of the humerus, facilitating shoulder extension.
- Innervated by the suprascapular nerve.
M. infraspinatus
- Originates from the infraspinous fossa of the scapula.
- Inserts on the major tubercle of the humerus, involved in shoulder flexion.
- Covered distally by the deltoid muscle and innervated by the suprascapular nerve.
M. deltoideus
- Divided into acromial and scapular parts.