Module 4 - The Muscular System PDF

VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 1 Module 4 The Muscular System Overview Muscles are organs that con...

VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 1 Module 4 The Muscular System Overview Muscles are organs that contract to produce movement. This module is focused mainly on the skeletal muscle of dog. Although detailed myology is available for study, this module will give you an overview of the common muscles observed during dissection with some information on their physiological and basic clinical importance. Take note that the topics were arranged per region of the body as it is the best presentation in most textbooks as well as it simulates the feeling of actual muscle dissection. I. Objectives 1. Identify the organization of a muscle fiber. 2. Identify the different muscles of the body. II. Learning Activities The bulk of the muscle in the body is skeletal muscle. Other types are smooth and cardiac muscles. A skeletal muscle is composed of organization of structures as shown below. Figure 1 Muscle structure (Aspinall and O’reilly, 2004) Endomysium - the connective tissue between individual muscle fibers Perimysium - the sheath surrounding bundles of muscle fibers Epimysium - the connective tissue around an entire muscle. It is the deep fascia of the muscle. EY Balagan Department of Morphophysiology and Pharmacology 1 College of Veterinary Science and Medicine Central Luzon State University  VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 2 Origin- the less movable; in the limbs, it is the more proximal attachment Insertion – the more movable; in the limbs, it is the more distal attachment Belly - thick fleshy central part of the muscle tissue Fleshy attachment – the apparent direct attachment of muscles to bone Tendinous attachment – the dense connective tissue connecting the spindle shape or pennate muscle to bone Aponeurotic attachment – the flat, tendinous sheet Figure 2 Origin and insertion of muscle, schematic. associated with flat muscles such as those of the (Aspinall and O'reilly, 2004) abdominal wall Intrinsic muscle - lie completely within one region of the body where they have their origin and insertion. They act on the bones in that part only. Extrinsic muscle - run from one region of the body to another and alter the position of the whole part DERIVATION OF MUSCLE NAMES Muscle name based on range of action depresses a part Abductor Muscle that moves a Rotator Muscle that turns a body part away from the part on its axis midline Supinator Muscle that rotates the Adductor Muscle that moves a palmar or plantar part toward the midline surface upward Flexor Muscle that bends a limb Pronator Muscle that rotates the at its joint or decreases palmar of plantar surface the joint angle downward Extensor Muscle that straightens Muscle name based on location a limb or increases the Pectoral Located on the chest joint angle Epaxial Located above the pelvic Levator Muscle that raises of axis elevates a part Intercostal Located between rib Depressor Muscle that lowers of Infraspinatus Located beneath the EY Balagan Department of Morphophysiology and Pharmacology 2 College of Veterinary Science and Medicine Central Luzon State University  VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 3 spine of the scapula toothed Supraspinatus Located above the spine Teres Muscles are cylindrical of the scapula No Rules Inferior Below or deep Sartorius Named because it flexes Superior Above and adducts the leg of a Medius Middle human to that position Externus Outside assumed by a tailor Internus Inside sitting cross-legged at Orbicularis Surrounding another work structures Gemellus Twinned muscle Muscle name based on direction Gastrocnemius Resembles shape of a Rectus Straight; align with the stomach vertical axis of the body Oblique Slanted; slant outward from the midline Transverse Crosswise Sphincter Tight band; ring-like and constrict the opening of passages Muscle name based on number of parts Biceps Generally have two divisions (heads) Triceps Generally have three divisions (heads) Quadriceps Generally have four divisions (heads) Azygous Not paired or income Muscle name based on size Minimus or Small minor Maximus, Large major or vastus Latissimus Broad Longissimus or Narrow gracilis Muscle name based on shape Deltoid Looks like Greek letter delta Quadratus Muscles that are square or four-sided Rhomboideus Muscles are diamond- shaped Scaleneus Muscles are unequally three-sided Serratus Muscles are saw- EY Balagan Department of Morphophysiology and Pharmacology 3 College of Veterinary Science and Medicine Central Luzon State University VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 4 Figure 3 Muscles of mastication, lateral view (Aspinall and O'reilly, 2004) MUSCLES OF HEAD Muscles of Mastication Those that have attachments to the mandible and whose contractions produce the jaw movements associated with chewing. As a general rule, considerably more muscle mass (and therefore strength) is devoted to the elevation (closure) of the mandible than to depression (opening). Most of the muscles of mastication are innervated by the trigeminal nerve. Digastricus (biventer)- only muscle that opens the jaw, aided by gravity. Masseter - closes the jaw and lies lateral to the mandible. It is located at the deep masseteric fossa of the mandible of dog. Temporalis - also closes the jaw and is the largest and strongest muscle of the head. It covers much of the dorsal and lateral surfaces of the skull. Medial and lateral pterygoids - these are deep muscles that lie medial to the mandible. They aid the temporalis and masseter muscles in closing the jaw, but they are also responsible for the side to side movement of the mouth typical of herbivore mastication. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 5 Figure 4 Superficial muscles of the head (Evans and De Lahunta, 2010) Muscles of Facial Expression The muscles that move the skin and appendages of the face and head are the muscles of facial expression or mimetic muscles. These are generally thin cutaneous muscles innervated by the facial nerve. Muscles of the Cheek 1. Platysma - the most superficial muscle of the face. Relatively well-developed sheet of muscle that draws the angle of the mouth caudally. 2. Buccinator (trumpeter’s muscle)- a thin, wide sheet of muscle that forms the non- cutaneus substance of the cheek. Its contraction draws the cheek inward against the teeth. Muscles of the Lips 1. Levator nasolabialis - also one of the most superficial muscle layer, covers the lateral surface of the nasal bone and maxilla, just deep to the skin. Contraction EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 6 causes the dilatation of the nostrils and raises the upper lip. 2. Orbicularis oris - lies deep in the platysma and levator nasolabialis. Its fibers run longitudinally around the opening of the mouth. Contraction closes the lips by drawing them together into the shape of an “O”. Figure 5 Deep muscles of the head (Evans and De Lahunta, 2010) 3. Maxillonasolabialis - a specialization of the dorsal part of the orbicularis oris. It is divided into 2 portions, both of which lie deep to the levator nasolabialis. Levator labii superioris - more dorsal portion. It raises the upper lip and dilates the nostrils (involved in Flehmen response) Caninus - the more ventral portion. Similar origin with the levator labii superioris but it inserts only into the upper lip. Contraction raises the upper lip 4. Zygomaticus (smiling muscle)- it draws the angle of the mouth caudally and external ear cranially and ventrally. 5. Mentalis - essentially a subdivision of the ventral part of the buccinators. Contraction stiffens the apical region of the lowerlip. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 7 Muscles of the Forehead 1. Frontalis - thin sheet of muscle overlying temporal bone. Contraction draws the scutular cartilage forward and raises the eyebrow. Muscles of the Eyelid 1. Orbicularis oculi - surrounds the palpebral fissure. Contraction closes the said fissure. 2. Retractor anguli oculi lateralis - passes directly caudally from the lateral palpebral angle to blend with the temporal fascia. It draws the lateral palpebral angle caudally thereby assisting in the closing of the eye. 3. Levator anguli oculi medialis - passes directly from the medial palpebral angle to attach to the frontal bone. It raises the upper lid and erects the hair of the eyebrow. 4. Levator palpebrae superioris - arises deep within the orbit and inserts into the upper eyelid. Contraction raises the eyelid. 5. Palpebral part of the deep sphincter of the neck - deep to the platysma. It depresses the lower eyelid. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 8 Figure 6 Extraocular muscles (Aspinall and O'reilly, 2004) Extraocular Muscles A number of striated muscles lie within the orbit associated with the globe of the eye. These extraocular muscles (so called because they are attached to the outside of the eyeball) move the globe of the eye in the many directions of which it is capable. Dorsal rectus - elevates globe Ventral rectus - depresses globe Medial rectus - turns globe nasally / medially Lateral rectus- turns globe temporally/ laterally Dorsal oblique - intorts globe (rotates 12o’clock position nasally) Ventral oblique - extorts globe (rotates 12o’clock position temporally) Retractor bulbi- retracts globe EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 9 Figure 7 Superficial muscles of the head, dorsal view (Evans and De Lahunta, 2010) MUSCLES OF THE EXTERNAL EAR The muscles of the ear can be grouped as extrinsic or intrinsic muscles. Extrinsic Ear Muscle 1. Rostral auricular muscle - superfcial scutuloauricularis, deep scutuloauricularis, frontoscutularis. frontalis and zygomaticoauricularis. 2. Dorsal auricular muscle – interscutularis, parietoscutularis, and parietoauricularis 3. Caudal auricular muscle – cervicoscutularis, superfcial cervicoauricularis, middle cervicoauricularis, deep cervicoauricularis, parotidoauricularis and styloauricularis. 4. Ventral auricular muscle - parotidoauricularis and styloauricularis Intrinsic Ear Muscle 1. Helicis 2. Helicis minor 3. Tragicus EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 10 Figure 8 Extrinsic muscles of the tongue (Evans and de Lahunta, 2010) MUSCLES OF THE TONGUE The muscles of the tongue include the styloglossus, hyoglossus, genioglossus, and lingual intrinsic muscles. These are all innervated by the hypoglossus nerve. The intrinsic muscles of the tongue are arranged in fascicles that run longitudinally, transversely, and vertically, allowing the tongue to change shape in multiple planes. Extrinsic muscles of the tongue are those that arise from outside the tongue, include: 1. Styloglossus – extends from the stylohyoid to the tongue. It has three muscle heads that inserts at the tongue at different level. It draws the tongue caudally. 2. Genioglossus- thin, triangular muscle at the intermandibular space ventral to the tongue. Contraction draws the entire tongue rostrally. It depresses the tongue. 3. Hyoglossus – located at the root of the tongue. It retracts and depresses the tongue. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 11 Figure 9 Epaxial and Hypaxial muscles (Aspinall and O'reilly, 2004) MUSCLES OF THE NECK AND BACK Both neck and back are provided with set of extrinsic and a set of intrinsic muscles. The intrinsic muscles of vertebral column are divided into two major groups, the epaxial and hypaxial muscle. The axis of reference is the vertebral column itself at the level of the transverse process. Epaxial muscles - positioned dorsal to the transverse process of the vertebra. Their function is to support the spine, extend the vertebral column and allow lateral flexion. Hypaxial muscles - positioned ventral to the transverse process of the vertebrae. They flex the neck and tail and contribute to the flexion of the vertebral column. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 12 Figure 10 Epaxial muscles of the neck, back and long area (Evans and Dela Hunta, 2010) Extensors of the Neck Epaxial muscles serve to extend the vertebral column and neck. They are arranged in three adjacent longitudinal groups: transversospinalis, longissimus and iliocostalis systems. 1. Transversospinalis system - most medial, lies directly to the vertebral bodies and spinous processes. It extends from the sacrum to the head. a. Spinalis et semispinalis cervicis - originates along the thoracic vertebral bodies and inserts on the spinous process of vertebrae C5 - C2 b. Semispinalis capitis - lies adjacent to the nuchal ligament and has two parts: biventer cervicis—more dorsal complexus - more ventral c. Multifidus cervicis - series of small, deeply placed muscle. It pass cranially from the midregion of one vertebra to the spinous process of the vertebra which they insert. d. Interspinales - tiny muscle that extend between adjacent spinous process, are distinct in the cervical region 2. Longissimus system - intermediate system, is the longest and strongest of the three. It extends from the wing of the ilium to the skull. a. Longissimus cervicis - direct continuation of the thoracic part b. Longissimus capitis - flattened yet relatively thick and strong muscle positioned fairly deeply. c. Longissimus atlantis - an inconstant muscle, when present this muscle is a deep slip of the longissimus capitis. d. Intertransversarius - set of muscles derived from deeper portions of the longissimus system. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 13 3. Iliocostalis system - the most lateral, extends from the ilium to C7. It can be easily identified in most region by the length of its flat, shiny tendons. This system is minimally represented in the neck; only its cranial-most belly extends so far. Flexors of the Neck 1. Sternocephalicus - flex the neck and joints of the head and draws the head and neck laterally. There are two divisions of this muscle which both arise from the sternum and insert on the head and neck. In their diverging paths, these two embrace the ventral and lateral surface of the neck in the form of letter “V”.  Sternomastoideus - more medial and inserts on the mastoid process of the skull  Sternooccipitalis - more lateral, thinner and flatter than the sternomastoideus. It inserts along the midline of the neck from the midcervical region cranially to the skull 2. Sternohyoideus (strap muscle) -thin, flat muscle that draws the basihyoid bone caudally. 3. Sternothyroideus (strap muscle) -draws the larynx and tongue caudally 4. Scalenus - flexes the neck ventrally and draws the neck laterally 5. Hypaxial muscles - act as ventral flexors of the neck and occipitoatlantal joint. a. Longus capitis - elongate, flattened muscle positioned on the ventrolateral surface of the cervical vertebrae and is the lateral-most of the intrinsic muscle of the neck muscles. b. Longus coli - composed of numerous segmental bundles located directly on the ventral surfaces of the vertebral bodies from C1 caudally as far as T6. Thus, it is divisible into cervical and thoracic portions. c. Rectus capitis ventralis - short yet strong muscle that flexes the atlantooccipital joint. d. Rectus capitis lateralis - small muscle positioned immediately lateral to the rectus capitis ventralis. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 14 Figure 11 Abdominal muscles (Aspinall and O'reilly, 2004) MUSCLES OF THE ABDOMEN The abdominal wall on each side of the body is composed of four muscles, which form broad flat sheets. Their fibers run in all directions, which gives the abdominal wall great strength. Most of these muscles have broad aponeurotic insertions that meet at the midventral line known as the linea alba (white line). 1. External abdominal oblique - most superficial. The fibers of this muscle lie obliquely ventrad and caudad. 2. Internal abdominal oblique - immediately deep to the external abdominal oblique muscle. Its fibers pass obliquely ventrad and craniad. 3. Transversus abdominis - is the deepest of the abdominal muscles. The fibers are directed perpendicular to the long axis of the body. 4. Rectus abdominis - forms the muscular floor of the abdomen. The fibers run directly caudad in a horizontal plane to attach to the pubis by means of a strong prepubic tendon. It is characteristically divided by a series of tendinous intersections. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 15 Figure 12 Superficial muscles of the thoracic limb (Evans and De Lahunta, 2010) MUSCLES OF THE THORACIC LIMB MUSCLES ACTING ON THE SHOULDER GIRDLE 1. Trapezius (Cucullaris) - is a flat triangular sheet of muscle. It is divided into two parts: Cervical part (trapezius cervicis) which is larger and the thoracic part (trapezius thoracis) which is smaller. The portion originating cranial to the scapula helps swing the scapula forward; the one attaching behind draws it back. 2. Rhomboideus - is a heavier muscle just deep to the trapezius. It is composed of three parts and inserts mainly on the medial dorsal border of the scapula.  Rhomboideus capitis - long, thin, strap–like muscle that originates on the occipital bone  Rhomboideus cervicis - more substantive than its capital part, but is also strap like. It originates in the cervical raphe  Rhomboideus thoracis - short, thick expanse of muscle of considerable substance. It originates on the spinous process of vertebra T4 - T7 EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 16 3. Serratus ventralis - is the largest and 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 limbs. 4. Omotransversarius - is a separate muscle of the shoulder region in most domestic species. It usually pulls the distal end of the scapula forward, although with the limb in weight bearing position, it instead assists lateral flexion of the neck. MUSCLES ACTING ON THE SHOULDER JOINT Extensors of the shoulder 1. Brachiocephalicus - extends from the head to the arm. It 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 and acts as a lateral flexor of the neck when the limb is weight bearing. It is subdivided into the cleidobrachialis, extending from the clavicular tendon (representing the vestigial clavicle) to the humerus, and the cleidocephalicus, extending from the clavicular tendon to the head and neck. Cleidocephalicus may be further subdivided into a mastoid part (cleidomastoideus) attaching to the mastoid process of the temporal bone and a cervical part (cleidocervicalis). 2. Supraspinatus - acts chiefly as a stabilizing ligament of the shoulder joint. This is one of the muscles that atrophies in sweeny in horses, a condition that results from damage to its motor innervation, the suprascapular nerve. Flexors of the shoulder 1. Infraspinatus - acts as a strong collateral ligament of the shoulder joint and may abduct, flex, and outwardly rotate the shoulder. This muscle also atrophies in cases of sweeny. 2. Teres major - a strong flexor of the shoulder joint. 3. Latissimus dorsi - is a wide, triangular muscle and is a strong flexor of the shoulder. Also, it pulls the thoracic limb caudad or, if the limb is fixed, advances the trunk. Known as the broadest muscle of the back. 4. Teres minor - lies just distal to the infraspinatus muscle and has the same action as the infraspinatus. 5. Deltoideus - extends from the spine of the scapula to the deltoid tuberosity of the humerus. It is an abductor and flexor of the shoulder joint. It has two parts, which fuse before they insert and act together as a single unit. a. Scapular part - thin and sheet like b. Acromial part - thicker and is fusiform in shape EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 17 Figure 13 Neck and pectoral muscles (Evans and De Lahunta, 2010) Adductors of the shoulders 1. Pectoral muscles - form the substance of the brisket. Commonly, they are divided into the superficial pectoral muscle and the deep pectoral muscle. These pectoral muscles are strong adductors of the forelimb, and the deep pectoral muscle also advances the trunk when the limb is fixed on the ground. 2. Coracobrachialis - is a small muscle in which the location of the muscle belly suggests a shoulder flexor, but its attachments make this muscle an extensor of that joint. 3. Subscapularis - stabilizes the shoulder on the medial side. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 18 Figure 14 Superficial muscles of thoracic limb, lateral view (Evans and De Lahunta, 2010) MUSCLES ACTING ON THE ELBOW Since the elbow is a hinge joint, the muscles acting on it are either flexors or extensors. In quadrupeds, the extensors are stronger than the flexors because they support the weight of the body by maintaining the limbs in extension. Extensors of the elbow 1. Triceps brachii - It fills the space between the scapula and humerus. It has three heads. The long head originates from the caudal border of the scapula, and the medial and lateral heads originate from the respective sides of the humeral diaphysis. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 19 Carnivores have an accessory head that also originates from the humerus between the medial and lateral heads. All heads insert on the olecranon process of the ulna. The triceps is the strongest extensor of the elbow. 2. Anconeus - deep to the triceps brachii, is a rather small muscle that covers the caudal aspect of the joint capsule of the elbow. It also originates on the humerus, inserts on the olecranon process, and extends the elbow. 3. Tensor fasciae antibrachii - the muscle’s name reflects its action on the antebrachial fascia (it tenses it), but through these fascial connections the tensor fasciae antibrachii also assists the triceps in extension of the elbow. Flexors of the elbow 1. Biceps brachii - assists in holding the shoulder joint in apposition and may extend it to some extent. However, the chief action is flexion of the elbow. The tendinous blending with the antebrachial fascia forms a Figure 15 Muscles of the thoracic limb, medial view (Evans and De palpable cordlike structure on the Lahunta, 2010) flexor surface of the elbow called the lacertus fibrosus. 2. Brachialis - strictly a flexor of the elbow 3. Pronator teres - acts primarily as a flexor of the elbow EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 20 MUSCLES ACTING ON THE CARPUS The carpus, like the elbow, acts essentially as a hinge joint. The extensors of the carpus lie on the craniolateral aspect of the limb, and the flexors are found on the caudomedial side. Extensors of the carpus 1. Extensor carpi radialis - largest extensor of the carpus. This is the most prominent muscle on the front of the forearm and is the most cranial muscle of the group. 2. Extensor carpi ulnaris (Ulnaris lateralis) - is the most caudal of the extensor muscles. In most domestic animals, this muscle probably produces weak flexion of the carpus, although by origin and nerve supply it belongs with the extensor group. It also produces some outward rotation of the forearm. 3. Extensor carpi obliquus (Abductor pollicis longus, abductor digiti I) - is a flat, triangular extensor of the carpus lying deep to the digital extensor muscles of the antebrachium. Figure 16 Muscles of the distal thoracic limb, cranial view Flexors of the carpus (Evans and De Lahunta, 2010) 1. Flexor carpi radialis - is just caudal to the radius, which is palpable directly beneath the skin. 2. Flexor carpi ulnaris - exerts considerable leverage as a flexor of the carpus by inserting on the accessory carpal bone, which projects in a palmar direction from the lateral aspect of the carpus. These muscles are, of course, primarily flexors of the carpus, but they may act slightly in extension of the elbow. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 21 MUSCLES ACTING ON THE DIGITS Extensors of the digits 1. 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 flexing the elbow. 2. Lateral digital extensor - is found in all species. The origin is on the lateral collateral ligament of the elbow and lateral radius and ulna. The insertion varies according to the number of digits present. Flexors of the digit 1. Deep digital flexor - lies the closest to the metacarpal bones. 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. 2. Superficial digital flexor - similar to the deep digital flexor but it inserts primarily on the proximal part of the middle phalanx of each digit. Interosseous - lie between the metacarpal bones of carnivores and humans. It is muscular in pigs and dogs but in large ungulates most of the muscle tissue has been replaced with connective tissue, and these structures are known as the suspensory ligaments or interosseous medius. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 22 Figure 17 Muscles of the proximal distal limb, lateral view (Evans and De Lahunta, 2010) MUSCLES OF THE PELVIC LIMB MUSCLES ACTING ON THE HIP JOINT Extensors of the hip 1. Hamstring muscles - chief extensors of the hip. They include the biceps femoris (the most lateral of the caudal muscles of the thigh), the semitendinosus (the middle muscle of the caudal group), and the semimembranosus (the medial muscle of this group). 2. Middle gluteal - another strong extensor of the hip. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 23 Figure 18 Muscles of the pelvic limb, medial view (Evans and De Lahunta, 2010) Flexors of the Hip 1. Iliopsoas - strongest muscle of the pelvic girdle. It is formed by the union of the iliacus and psoas major. 2. Sartorius - is a thin, straplike muscle that extends from the tuber coxae to the tibia, diagonally crossing the medial surface of the thigh. It is divided into two distinct parts in dogs, sartorius cranialis and sartorius caudalis. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 24 Abductors of the hip 1. Deep gluteal - extends from the spine of the ischium laterad over the hip joint to insert on the greater trochanter. 2. Superficial gluteal - extends from the sacral vertebral spines to the third trochanter just distal to the greater trochanter. Considerably a weak muscle in domestic animals. 3. Tensor fasciae latae - it is a strong, fan-shaped pyramid which extends from the tuber coxae to the lateral femoral fascia, which attaches to the patella. In addition to abducting the hip joint, this muscle flexes the hip joint and extends the stifle. Adductors and Rotators of the hip 1. Gracilis - is the most medial muscle extending from the symphysis of the pelvis to the tibia. 2. Pectineus - a small spindle-shaped muscle deep to the gracilis, is both an adductor and flexor of the hip. 3. Adductor - is the largest muscle on the medial side of the thigh. It extends from the ventral aspect of the pelvis to the medial side of the femur and tibia. It is a strong adductor but may also help to extend the hip. It is divided into a bigger adductor magnus and a smaller adductor longus. 4. Quadratus femoris - is an adductor of the thigh. Several other small muscles in this deep layer of hip musculature extending from the area of the obturator foramen are outward rotators of the thigh. They include the internal and external obturator muscles and the gemelli. MUSCLES ACTING ON THE STIFLE Extensors of the stifle 1. Quadriceps femoris - one large muscle, and is the primary extensor of the stifle. This muscle has four heads; their distinct origins and clearly distinguishable muscle bellies make it common practice to name them as separate muscles. All four heads insert on the patella.  Rectus femoris - the strongest and longest head, originates from the ilium just above the acetabulum.  Vastus medialis - originates in medial shaft of the femur  Vastus intermedius - originates in between medial and lateral shaft of the femur  Vastus lateralis - originates in lateral shaft of the femur EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 25 Flexors of the stifle NOTE: The chief flexors of the stifle are the hamstring muscles, which also extend the hip. In addition, the extensor muscles of the hock that originate on the caudal surface of the distal end of the femur may also flex the stifle. These muscles include the gastrocnemius and the superficial digital flexor. 1. Popliteus - is a relatively small muscle caudal to the stifle. Its chief action is flexion of the stifle, although it may slightly rotate the leg medially. MUSCLES ACTING ON THE HOCK Extensors of the hock 1. Gastrocnemius - forms the largest bulge of the caudal crus. This is the most superficial muscles in the caudal crus and is comprise of a medial and a lateral head. The tendons of gastrocnemius and superficial digital flexor make up the bulk of the common calcanean tendon or the Tendon of Achilles. 2. Soleus - blends distally with the lateral head of the gastrocnemius. Absent in dog and mostly developed in pigs. The gastrocnemius and soleus muscle are commonly fused together and are termed Triceps surae or the triceps of the calf. Flexors of the hock 1. Tibialis cranialis - most superficial muscle on the cranial crural surface and is fleshy throughout most of its length. 2. Peroneus brevis - has short fibers that remain closely applied to the lateral tibial and fibular surfaces. This muscle is found only in carnivores and is a weak muscle. 3. Peroneus longus - located just cranial to the fibula. It acts to pronate the foot. 4. Peroneus tertius -. Together with the superficial digital flexor, they constitute the reciprocal apparatus. MUSCLES ACTING ON THE DIGITS Extensors of the digit 1. Long digital extensor 2. Lateral digital extensor - lies between the extensor and flexor groups of muscles of the crus. 3. Long extensor of the hallux EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 26 Flexors of the digit 1. Superficial digital flexor - a spindle-shaped muscle sandwiched between the two heads of the gastrocnemius superficially and the popliteus and deep digital flexor muscle deeply. Owing to a shared point of origin, much of the proximal part is fused with the lateral head of the gastrocnemius. 2. Deep digital flexor - lies against the caudal tibial surface. It is a composite of three parts lateral and medial digital flexor and ulnaris caudalis. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 27 III. Assessment Identify the choice that best completes the statement or answers the question. 1. The following are members of the hamstring muscle, EXCEPT: A. biceps femoris B. semitendinosus C. semimembranosus D. quadriceps femoris 2. How many heads are present in the triceps brachii of dog? A. 1 B. 2 C. 3 D. 4 3. The deltoideus muscle is composed of the scapular part and what other part? A. spinous part B. acromial part C. glenoid part D. humeral part 4. The common calcanean tendon, or the Tendon of Achilles, is a tendon fused from gastrocnemius and which other muscle? A. deep digital flexor B. superficial digital flexor C. biceps femoris D. quadriceps femoris 5. What is the thickened structure at the distal end of the scapular spine? A. Acromion B. Coracoid process C. Subscapular fossa D. Glenoid cavity 6. The following are epaxial muscles, EXCEPT: A. longissimus B. iliocostalis C. transversospinalis D. longus coli 7. Which of the abdominal muscles is the deepest? A. External abdominal oblique B. Internal abdominal oblique C. Rectus abdominis D. Transversus abdominis EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine VANA 2200 – Gross Veterinary Anatomy Module 4 The Muscular System Page | 28 8. What structure divides the cleidocephalicus and cleidobrachialis? A. Clavicular tendon B. Anconeal muscle C. Deltoid tuberosity D. Tubercle of the rib 9. What is the smiling muscle? A. Zygomaticus B. Caninus C. Levator nasolabialis D. Trapezius 10. What muscle fills the subscapular fossa? A. Subscapularis B. Suprascapularis C. Infrascapularis D. Deltoideus References  Aspinall, V and M. O’Reilly. 2004. Introduction to Veterinary Anatomy and Physiology. 1st Ed. Elsevier Limited. UK  Evans, H. E and A. de Lahunta. 2010. Guide to the Dissection of the Dog. 7th ed. Saunders Elsevier. Philadelphia.  Frandson, R. D., W. L. Wilke, and A. D. Fails. 2009. Anatomy and Physiology of Farm Animals. 7th ed. Wiley– Blackwell. USA  König, H. E. And H G. Liebich. 2004. Veterinary Anatomy of Domestic Animals. Textbook and Colour Atlas. Stuttgart, Germany, Schattauer Gmbh  Pasquini and Spurgeon. 1987. Anatomy of Domestic Animals: Systemic and Regional Approach. 5th ed. Sudz publishing co. U. S. A. EY Balagan Department of Morphophysiology and Pharmacology Central Luzon State University College of Veterinary Science and Medicine