Thoracic Limb Muscles Overview

Welcome to Part 3 of Module 4. This part of presentation will be dealing with the muscles of the thoracic limb. The muscles of the thoracic limb are composed of intrinsic and extrinsic muscles. As I recall, an intrinsic muscle lies completely within one region of the body where they have their origin and insertion, in this case, the bones of the thoracic limb. On the other hand, Extrinsic muscles run from one region of the body to another. Moreover, the muscles can be grouped further based on which joint of the limb they are acting with. This include the muscles of the shoulder girdle, muscles of the shoulder joint, the elbow, muscles of the carpus and the muscles of the digits. In addition, the muscles within the grouping are subgrouped further as to whether they are an extensor, a flexor, an adductor or abductor. Let us begin with the muscles acting on the shoulder girdle. The first muscle is a flat triangular sheet of muscle as shown here. This is the trapezius muscle. It is divided into two parts. A cervical part or the trapezius services is larger compared to the thoracic part or the trapezius thoraces which is smaller. This muscle helps swing the scapula forward and backward. The next muscle is the rhomboideus. If the trapezius is removed or reflected, the rhomboideus muscle can be seen. This is a heavier muscle just deep to the trapezius. It is composed of three parts and were named based on their area at the neck region. Rhomboideus capitis is a long, thin, strap-like muscle that originates on the occipital bone. Rhomboideous cervices has more substance and originates at the cervical raphe. Rhomboideous thoracis is a short, thick, expansive muscle. It originates on the spinous process of the thoracic vertebrae 4 to 7. Serratus ventralis is the largest and the most important muscle attaching the thoracic limb to the trunk. It is a large, fan-shaped muscle. It forms a sling that supports the trunk between the thoracic limb. Take note that in this image, the trapezius and the latissimus dorsi muscles were reflected to show the serratus ventralis muscle. Homo transversarius is a separate muscle of the shoulder region. It usually pulls the distal end of the scapula forward, although with the limb in weight-bearing position, it instead assists a lateral flexion of the neck. Now let us discuss the muscles of the shoulder joint. Muscles under this section is divided based on their main action. Let us begin with the extensors. First is the brachiocephalicus muscle. From the name itself, it extends from the head or cephalic to the arm or brachium. This is a heavy muscle covering the cranial aspect of the point of the shoulder. It raises and advances the shoulder. It is the principal extensor of the shoulder area and acts as a flexor of the neck when the limb is weight-bearing. This muscle is subdivided into clidobrachialis, extending from the clavicular tendon to the humerus, and clidosephalicus, extending from the clavicular tendon to the head and neck. Clidosephalicus may be further subdivided into a mastoid part or the clidomastoidus, attaching to the mastoid process of the temporal bone, and a cervical part or the clidoservicalis. Remember that the clavicular tendon represents the vestigial clavicle. Supraspinatus acts chiefly as a stabilizing ligament of the shoulder joint. This is a deep muscle attached to the supraspinous fossa. For the flexors of the shoulder joint, Let us begin with the latissimus dorsi. This is a wide triangular muscle and is a strong flexor of the shoulder. Also, it pulls the thoracic limb caudally or if the limb is fixed, it advances the trunk. It is also known as the broadest muscle of the back. The next flexor is the deltoidius muscle. This muscle extends from the spine of the scapula to the deltoid tuberosity of the humerus. It has two parts which fuse before they insert and act together as a single unit. The scapular part is the thin and sheet-like. while the acromial part is thicker and is fusiform in shape. The infraspinatus muscle acts as a strong collateral ligament of the shoulder joint and may abduct, flex, and outwardly rotate the shoulder. This muscle is located filling the space of the infraspinus fossa. The teres major, as shown here, is also a strong flexor of the shoulder joint. The brachium is removed to show more of the infraspinatus and the teres major muscles. Also part of the flexor of the shoulder is the teres minor muscle. This muscle lies just distal to the infraspinatus muscle and has the same action with the infraspinatus. Now let us discuss the adductors of the shoulder. Pectoral muscles form the substance of the brisket. Commonly, they are divided into the superficial pectoral muscle and the deep pectoral muscle the deep pectoral muscle is also termed as the ascending pectoral muscle because of the ascending fashion of the muscle fibers on the other hand the superficial pectoral muscle is further subdivided into a descending part and a transverse part the pectoral muscles are strong adapters of the forelimb and the deep pectoral muscle also advances the trunk when the limb is fixed on the ground to see other adapters of the shoulder here is a medial view of the scapular region the subscapularis muscle stabilizes the shoulder on the medial side this muscle fills the space of the subscapular fossa the coracobrachialis on the other hand is a small muscle in which the location of the muscle belly suggests that it is a shoulder flexor but its attachment makes it a muscle of an extensor of that joint. Now let us move to the muscles acting on the elbow. Since the elbow is a hinge joint, the muscles acting on it are either flexors or extensors. In general, the extensors are located at the lateral side while the flexors are seen at the medial side of the limb. In quadrupeds, the extensors are stronger than the flexors because they support the weight of the body by maintaining the limb in extension position the first muscle is the triceps brachii muscle it is the strongest extensor of the elbow it fills the space between the scapula and the humerus from the name itself it has three heads however in dogs four heads are present shown here is the long head which originates from the caudal border of the scapula, the lateral head which originates from the lateral humeral diaphysis. To see the other heads of the triceps brachii, here is a dissected arm showing the medial and lateral side. For orientation purposes, here is the long head and the lateral head which were previously discussed. Take note that the lateral head is reflected. this time. The medial head originates from the medial humeral diaphysis. The fourth and the additional head in carnivores like dog is the accessory head. It originates from the humerus between the medial and the lateral heads. Take note that all heads inserts on the olecranon process of the ulna. Deep to the triceps brachii is a rather small muscle called anconius. It covers the caudal aspect of the joint capsule of the elbow. Next is the tensor fascia antebrachii. The muscle's name reflects its action on the antebrachial fascia, or it tenses it. But through these fascial connections, the tensor fascia antebrachii also assist the triceps in the extension of the elbow. As mentioned, most of the flexors are located at the medial side of the limb. One of the flexors of the elbow is the biceps brachii. This muscle assists in holding the shoulder joint in a position and may extend it to some extent. However, the chief action is flexion of the elbow. Also classified as flexors are the brachialis and the pronator teres muscle. The carpus and digits, like the elbow, act essentially as a hinge joint. The extensors of the carpus lie on the cranial lateral aspect of the limb, while the flexors are found on the caudomedial side of the limb. Here are the muscles of the antebrachium in a lateral, cranial, medial, and caudal view for better visualization. Take note that the muscle action is not strictly on a certain joint. For example, a muscle can be an extensor of the carpus but a flexor of the elbow. What we will point out in this presentation is their main action. The first muscle is the extensor carpi radialis. This is the largest extensor of the carpus. This is also the most prominent muscle on the front of the forearm and is the most cranial muscle of the group. The common digital extensor is the longest extensor muscle in the thoracic limb. This muscle is an extensor of all joints of the digit including the fetlock. It may also assist in extending the carpus and even in the flexing of the elbow. The lateral digital extensor originates on the lateral collateral ligament of the elbow and lateral radius and ulna. The insertion varies according to the number of digits present. In the case of dog, it has five insertions. The extensor carpi ulnaris is formerly known as the ulnaris lateralis. It is the most caudal of the extensor muscles. In most domestic animals, This muscle probably produce a weak flexion of the carpus, although by origin and nerve supply, it belongs to the extensor group. It also produces some outward rotation of the forearm. The extensor carpi obliquus or the abductor pollicis longus or the abductor digiti 1 is a flat triangular extensor of the carpus lying deep to the digital extensor muscles of the antebrachium. As you observed, most of the extensors are seen at the lateral side of the antebrachium. For the flexors, same views of the antebrachial muscles are shown. Let us first locate the flexor carpi radialis. This is caudal to the radius which is palpable directly beneath the skin. The flexor carpi ulnaris exerts considerable leverage as a flexor of the carpus. by inserting on the accessory carpal bone. It projects in a palmar direction from the lateral aspect of the carpus. These muscles are of course primarily a flexor of the carpus but they may act slightly in the extension of the elbow. There are two digital flexors. Here is the superficial digital flexor and a deeper dissection is needed to expose the deep digital flexor as shown here. It lies the closest to the metacarpal bone. It is the only muscle that flexes the distal interphalangeal joint. Secondarily, it also flexes the more proximal joints of the digit and the carpus. It is also important in supporting the fetlock. And that concludes our presentation on Part 3 of Module 4. Just a point to remember, the action of each muscle is not exclusive to a particular joint. It can be an extensor of a proximal joint but a flexor of a more distal joint. You may now proceed to part 4 of this module which is focused on the muscles of the pelvic limb.

On the other hand, Extrinsic muscles run from one region of the body to another. Moreover, the muscles can be grouped further based on which joint of the limb they are acting with. This include the muscles of the shoulder girdle, muscles of the shoulder joint, the elbow, muscles of the carpus and the muscles of the digits.

In addition, the muscles within the grouping are subgrouped further as to whether they are an extensor, a flexor, an adductor or abductor. Let us begin with the muscles acting on the shoulder girdle. The first muscle is a flat triangular sheet of muscle as shown here.

This is the trapezius muscle. It is divided into two parts. A cervical part or the trapezius services is larger compared to the thoracic part or the trapezius thoraces which is smaller.

This muscle helps swing the scapula forward and backward. The next muscle is the rhomboideus. If the trapezius is removed or reflected, the rhomboideus muscle can be seen. This is a heavier muscle just deep to the trapezius. It is composed of three parts and were named based on their area at the neck region.

Rhomboideus capitis is a long, thin, strap-like muscle that originates on the occipital bone. Rhomboideous cervices has more substance and originates at the cervical raphe. Rhomboideous thoracis is a short, thick, expansive muscle.

It originates on the spinous process of the thoracic vertebrae 4 to 7. Serratus ventralis is the largest and the most important muscle attaching the thoracic limb to the trunk. It is a large, fan-shaped muscle. It forms a sling that supports the trunk between the thoracic limb.

Take note that in this image, the trapezius and the latissimus dorsi muscles were reflected to show the serratus ventralis muscle. Homo transversarius is a separate muscle of the shoulder region. It usually pulls the distal end of the scapula forward, although with the limb in weight-bearing position, it instead assists a lateral flexion of the neck. Now let us discuss the muscles of the shoulder joint. Muscles under this section is divided based on their main action.

Let us begin with the extensors. First is the brachiocephalicus muscle. From the name itself, it extends from the head or cephalic to the arm or brachium. This is a heavy muscle covering the cranial aspect of the point of the shoulder.

It raises and advances the shoulder. It is the principal extensor of the shoulder area and acts as a flexor of the neck when the limb is weight-bearing. This muscle is subdivided into clidobrachialis, extending from the clavicular tendon to the humerus, and clidosephalicus, extending from the clavicular tendon to the head and neck.

Clidosephalicus may be further subdivided into a mastoid part or the clidomastoidus, attaching to the mastoid process of the temporal bone, and a cervical part or the clidoservicalis. Remember that the clavicular tendon represents the vestigial clavicle. Supraspinatus acts chiefly as a stabilizing ligament of the shoulder joint. This is a deep muscle attached to the supraspinous fossa. For the flexors of the shoulder joint, Let us begin with the latissimus dorsi.

This is a wide triangular muscle and is a strong flexor of the shoulder. Also, it pulls the thoracic limb caudally or if the limb is fixed, it advances the trunk. It is also known as the broadest muscle of the back. The next flexor is the deltoidius muscle. This muscle extends from the spine of the scapula to the deltoid tuberosity of the humerus.

It has two parts which fuse before they insert and act together as a single unit. The scapular part is the thin and sheet-like. while the acromial part is thicker and is fusiform in shape.

The infraspinatus muscle acts as a strong collateral ligament of the shoulder joint and may abduct, flex, and outwardly rotate the shoulder. This muscle is located filling the space of the infraspinus fossa. The teres major, as shown here, is also a strong flexor of the shoulder joint. The brachium is removed to show more of the infraspinatus and the teres major muscles. Also part of the flexor of the shoulder is the teres minor muscle.

This muscle lies just distal to the infraspinatus muscle and has the same action with the infraspinatus. Now let us discuss the adductors of the shoulder. Pectoral muscles form the substance of the brisket.

Commonly, they are divided into the superficial pectoral muscle and the deep pectoral muscle the deep pectoral muscle is also termed as the ascending pectoral muscle because of the ascending fashion of the muscle fibers on the other hand the superficial pectoral muscle is further subdivided into a descending part and a transverse part the pectoral muscles are strong adapters of the forelimb and the deep pectoral muscle also advances the trunk when the limb is fixed on the ground to see other adapters of the shoulder here is a medial view of the scapular region the subscapularis muscle stabilizes the shoulder on the medial side this muscle fills the space of the subscapular fossa the coracobrachialis on the other hand is a small muscle in which the location of the muscle belly suggests that it is a shoulder flexor but its attachment makes it a muscle of an extensor of that joint. Now let us move to the muscles acting on the elbow. Since the elbow is a hinge joint, the muscles acting on it are either flexors or extensors.

In general, the extensors are located at the lateral side while the flexors are seen at the medial side of the limb. In quadrupeds, the extensors are stronger than the flexors because they support the weight of the body by maintaining the limb in extension position the first muscle is the triceps brachii muscle it is the strongest extensor of the elbow it fills the space between the scapula and the humerus from the name itself it has three heads however in dogs four heads are present shown here is the long head which originates from the caudal border of the scapula, the lateral head which originates from the lateral humeral diaphysis. To see the other heads of the triceps brachii, here is a dissected arm showing the medial and lateral side. For orientation purposes, here is the long head and the lateral head which were previously discussed. Take note that the lateral head is reflected.

this time. The medial head originates from the medial humeral diaphysis. The fourth and the additional head in carnivores like dog is the accessory head.

It originates from the humerus between the medial and the lateral heads. Take note that all heads inserts on the olecranon process of the ulna. Deep to the triceps brachii is a rather small muscle called anconius.

It covers the caudal aspect of the joint capsule of the elbow. Next is the tensor fascia antebrachii. The muscle's name reflects its action on the antebrachial fascia, or it tenses it. But through these fascial connections, the tensor fascia antebrachii also assist the triceps in the extension of the elbow.

As mentioned, most of the flexors are located at the medial side of the limb. One of the flexors of the elbow is the biceps brachii. This muscle assists in holding the shoulder joint in a position and may extend it to some extent. However, the chief action is flexion of the elbow.

Also classified as flexors are the brachialis and the pronator teres muscle. The carpus and digits, like the elbow, act essentially as a hinge joint. The extensors of the carpus lie on the cranial lateral aspect of the limb, while the flexors are found on the caudomedial side of the limb. Here are the muscles of the antebrachium in a lateral, cranial, medial, and caudal view for better visualization. Take note that the muscle action is not strictly on a certain joint.

For example, a muscle can be an extensor of the carpus but a flexor of the elbow. What we will point out in this presentation is their main action. The first muscle is the extensor carpi radialis. This is the largest extensor of the carpus.

This is also the most prominent muscle on the front of the forearm and is the most cranial muscle of the group. The common digital extensor is the longest extensor muscle in the thoracic limb. This muscle is an extensor of all joints of the digit including the fetlock. It may also assist in extending the carpus and even in the flexing of the elbow. The lateral digital extensor originates on the lateral collateral ligament of the elbow and lateral radius and ulna.

The insertion varies according to the number of digits present. In the case of dog, it has five insertions. The extensor carpi ulnaris is formerly known as the ulnaris lateralis. It is the most caudal of the extensor muscles. In most domestic animals, This muscle probably produce a weak flexion of the carpus, although by origin and nerve supply, it belongs to the extensor group.

It also produces some outward rotation of the forearm. The extensor carpi obliquus or the abductor pollicis longus or the abductor digiti 1 is a flat triangular extensor of the carpus lying deep to the digital extensor muscles of the antebrachium. As you observed, most of the extensors are seen at the lateral side of the antebrachium. For the flexors, same views of the antebrachial muscles are shown.

Let us first locate the flexor carpi radialis. This is caudal to the radius which is palpable directly beneath the skin. The flexor carpi ulnaris exerts considerable leverage as a flexor of the carpus. by inserting on the accessory carpal bone. It projects in a palmar direction from the lateral aspect of the carpus.

These muscles are of course primarily a flexor of the carpus but they may act slightly in the extension of the elbow. There are two digital flexors. Here is the superficial digital flexor and a deeper dissection is needed to expose the deep digital flexor as shown here.

It lies the closest to the metacarpal bone. It is the only muscle that flexes the distal interphalangeal joint. Secondarily, it also flexes the more proximal joints of the digit and the carpus. It is also important in supporting the fetlock. And that concludes our presentation on Part 3 of Module 4. Just a point to remember, the action of each muscle is not exclusive to a particular joint.

It can be an extensor of a proximal joint but a flexor of a more distal joint. You may now proceed to part 4 of this module which is focused on the muscles of the pelvic limb.

Transcript for:Thoracic Limb Muscles Overview

Transcript for:
Thoracic Limb Muscles Overview