Dissection of the forelimb

• Skin incisions


  1. Incision 1: Longitudinal incision along the vertebral column

  2. Incision 2: Vertical incision extending from incision (1) to the elbow

  3. Incision 3: Circular incision around the elbow joint

  4. Incision 4: Longitudinal incision connecting incision (2) to the cranial aspect of the shoulder

  5. Incision 5: Incision parallel to incision (2) and extends from the caudal end of incision (1) to reach the midline of the ventral abdominal wall
• Cutaneous trunci


  • A thin muscular sheet, covering most of the dorsal, lateral and ventral walls of the thorax and abdomen
  • Closely applied to the skin
• Extrinsic muscles of the forelimb

  Muscles that attach the forelimb to the body wall
• Brachiocephalicus


  Has three parts: Cleidobrachialis, Cleidocervicalis, Cleidomastoideus
• When the foot rests on the ground Possible actions of the brachiocephalicus muscle.

  The muscle primarily stabilizes the shoulder joint and supports the weight of the body.
• When the limb is free to move Possible actions of the brachiocephalicus muscle

  To advance the limb; to extend the shoulder joint, and draw the head and neck to the side.
• Trapezius


  • Consists of a cervical and a thoracic part, separated by an aponeurosis
  • Can elevate and abduct the forelimb
• Omotransversarius


  • Strap-like muscle extending from the dorsal end of the spine of the scapula to the wing of the atlas
  • Can either advance the limb or flex the neck laterally .Innervation- Accessory nerve.
• Latissimus dorsi


  • Triangular shaped muscle with origin from the thoracolumbar fascia and last 7-8 thoracic vertebrae, and muscular origin from last 2-3 ribs
  • Inserts on the teres major tuberosity of the humerus
  • Draws the free limb caudally (as in digging) and the trunk forward during locomotory effort
  • Can also flex the shoulder
• Deltoideus


  • Composed of two portions: proximal portion originates from the spine of the scapula, distal portion arises from the acromion
  • Both portions fuse before insertion on the deltoid tuberosity of the humerus
  • Flexes the shoulder
• Dissection steps


  1. Cut the trapezius at its origin on the spine of the scapula

  2. Cut the two heads of the deltoids at their origin at the spine of the scapula

  3. Transect the cleidocervicalis just above the clavicular tendon

  4. Transect the omotransversarius

  5. Extend the skin incision (5) up to the ventral midline of the body wall and complete the circular incision (3) at the elbow on the medial aspect

  6. Lift the external jugular vein in the neck region and observe the jugular furrow

  7. Cut the sternocephalicus muscle at its insertion

  8. Cut the latissimus dorsi near the brachium
• Rhomboideus


  • Has three parts: rhomboideus capitis, cervicis and thoracis
  • Elevates the limb
• Serratus ventralis


  • Fan shaped muscle that acts like a sling in supporting the body
  • Originates from the transverse processes of the last five cranial vertebrae and the first seven or eight ribs, and inserts onto the serrated face of the scapula
• Superficial pectoral


  • Divided into a descending part and a transverse part
  • Originates from the first sternebra and first 2-3 sternebrae respectively, and inserts on the crest of the greater tubercle of the humerus
• Deep pectoral


  • Originates from the ventral part of the sternum and inserts on the lesser tubercle of the humerus, and has an aponeurotic insertion on the greater tubercle and its crest
• Detachment of the forelimb

  1. Cut the rhomboideus, serratus ventralis, pectorals, and cleidobrachialis near their attachments to the limb

  2. Abduct the limb to view the axillary region

  3. Observe the axillary artery, axillary vein, and the brachial plexus

  4. Cut the above-mentioned vessels and nerves close to the body wall
• The network of nerves formed is referred to as the brachial plexus
• Axillary artery


  Begins at the level of the first rib and extends up to the region of the connected tendons of the teres major and latissimus dorsi. It is the continuation of the subclavian artery and it continues into the brachium region as the brachial artery
• Arterial branches arising from the axillary artery

  • External thoracic
  • Lateral thoracic
  • Subscapular
  • Cranial circumflex humeral
• Axillary vein


  The main venous drainage of the forearm and it is a continuation of the brachial vein in the brachial region. It also receives an anastomosing branch from the cephalic vein. It ends up as the subclavian vein in the thoracic cavity
• Muscles found on the medial aspect of the scapula

  • Subscapularis
  • Remnant of serratus ventralis
  • Remnant of rhomboideus
  • Teres major
  • Region of insertion of supraspinatus
• Subscapularis


  Covers the entire space of the subscapular fossa. It inserts on the lesser tubercle of the humerus and thereby it adducts and extends the shoulder
• Teres major


  A band-like, straight muscle situated caudal to the subscapularis. It arises from the subscapularis and the proximal part of the caudal border of the scapula. It has attachment to the tendon of insertion of the lattissimus dorsi and is inserted on the teres major tuberosity of the humerus. The muscle flexes the shoulder joint. A branch of subscapular artery, which are called as thoracodorsal, supplies parts of teres major.
• Nerves of the brachial plexus to study


  • Suprascapular N. (C6, C7)
  • Subscapular N. (C6, C7)
  • Axillary N. (C7, C8)
  • Musculocutaneous N. (C6, C7, C8)
  • Radial N. (C7, C8, T1, T2)
  • Median N. (C8, T1, T2)
  • Ulnar N. (C8, T1, T2)
  • Thoracodorsal N. (C7, C8)
  • Lateral thoracic N. (T1, T2)
  • Pectoral N. (T1, T2)
• Suprascapular nerve


  Runs between the supraspinatus and the subscapularis near the neck of the scapula. It supplies the extensors of the shoulder joint
• Axillary nerve


  Enters the space between the subscapularis and the teres major, just caudal to the shoulder joint. It supplies the flexors of the shoulder joint
• Musculocutaneous nerve


  Long and lies cranial to the vessels in the brachial region. It supplies the muscles seen in the craniomedial aspect of the brachium
• Radial nerve


  The largest of the brachial nerves. It runs along with the median and ulnar nerves a short distance and then separates and enters a muscular groove distal to the teres major. The nerve supplies the extensors of the elbow, carpal and phalangeal joints
• Median and Ulnar nerves

  Have a common trunk between the brachial artery and brachial vein in the brachial region. These nerves supply the flexors of the carpal and phalangeal joints
• Muscles found on the medial aspect of the brachium

  • Biceps brachii
  • Tensor fasciae antibrachii
  • Brachialis
  • Medial head of the Triceps
  • Coracobrachialis
• Supraspinatus


  Found in the supraspinous fossa and is closely united with the subscapularis at the cranial border of the scapula. The entry of the suprascapular nerve into the muscle and also the insertion of the muscle on the greater tubercle of the humerus. The muscle extends and stabilizes the shoulder
• Infraspinatus


  Lies in the infraspinous fossa. The tendon of insertion (distal to the lesser tubercle of the humerus) can be located just distal to the acromion of the spine of the scapula and at the acetabular angle of the scapula. A synovial bursa lies underneath this tendon and over the greater tubercle of the humerus. The muscle can either flex or extend and abduct the shoulder joint depending on the degree of extension or position of this joint when the muscle contracts
• Teres minor


  A small wedge-shaped muscle found caudal to the shoulder. It lies between the infraspinatus and the triceps. It arises from the distal third of the caudal border of the scapula and inserts on the teres minor tuberosity of the humerus. This muscle flexes the shoulder joint
• Heads of the Triceps brachii

  • Long head
  • Lateral head
  • Medial head
  • Accessory head
• Long head of Triceps

  Has two bellies and it originates for the caudal border of the scapula. This inserts on the olecranon in common with the other heads of the triceps. Action is to extend the elbow and flex the shoulder. Innervation by radial nerve.
• Lateral head of Triceps


  Lies distal the proximal belly of the long head and cranial to the distal belly. It originates from the tricipital line of the humerus
• Accessory head of Triceps

  Bulkier than the lateral head and is intimately fused with the medial head. It originates from the neck of the humerus
• Medial head of Triceps

  Found immediately caudal to the humerus and comes in direct contact with the brachial vessels, median, ulnar, and musculocutaneous nerves on the medial aspect. It originates from the crest of the lesser tubercle near the teres major tuberosity
• Radial nerve pathway


  Can be observed from the medial aspect to the lateral aspect of the brachial region. It can be seen between the medial and accessory heads on entering the triceps and then passes distally between the brachialis muscle and the medial head and under cover by the accessory head. The muscular branches of the radial nerve supply the various heads of the triceps. The radial nerve terminates as a deep and a superficial branch on the lateral side, at the distal third of the brachium
• Brachialis


  A long thin muscle that lies in the brachialis groove of the humerus. It originates from the proximal third of the lateral surface of the humerus and inserts on to the ulnar and radial tuberosities. Actions is to flex the elbow. Innervation by musculocutaneous nerve.