Extrinsic Muscles of the Thoracic (or Pectoral) Limb

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Extrinsic Muscles of the Thoracic (or Pectoral) Limb

(Muscles that attach the thoracic limb to the body)



Origin (or Attachments)


N. Supply


Clinical note*** The following 4 muscles attach to the scapula. Scapulectomy would require cutting these 4 muscles


1. Cervical

2. Thoracic

1. Median fibrous raphe of the neck

2. Supraspinous ligament and dorsal spines of thoracic vertebrae 1-9

Spine of the scapula

Dorsal branch of the accessory (CN X1) n.

Elevate and draw the limb forward

Serratus ventralis

1. Cervical

2. Thoracic

1. Transverse processes of last 3 cervical vertebrae
2. Lateral surface of the ribs 1-8

Serrated face of the scapula

1. Ventral branches of last 3 cervical spinal nerves

2. Long thoracic n. of the brachial plexus

Passive support of the trunk; thoracic part aids inspiration; moves scapula forward and back


Wing of the atlas

Lower spine of scapula

Accessory (CN XI) n.

Draws scapula forward


1. Capitis (only in carnivores)

2. Cervical

3. Thoracic

1. Occipital bone of skull
2. Fibrous raphe of neck, spines of thoracic vertebrae

3. Spines of thoracic vertebrae (4-6)

Ventral branches of cervical and thoracic spinal nerves

Elevate the limb; move scapula forward, backward, and pull it close to the trunk

Clinical note*** The following 3 muscles attach to the humerus. Removal of the limb distal to the shoulder joint would require cutting these 3 muscles

Latissimus dorsi

Thoracodordal fascia via aponeurosis, lateral surface of last 3 ribs

Teres tubercle on the medial shaft of the humerus

Thoracodorsal nerve of the brachial plexus

Draw the limb backwards; flex the shoulder joint


1. Cleidobrachialis
2. Cleidocephalicus



1. Distal part of humeral crest

Cranial half of cervical raphe

Mastoid part of skull

1. Nerve of the brachiocephalicus (from the Brachial Plexus)

2. Ventral branches of several cervical nerves as well as accessory n.

Draw limb forward, acting bilaterally; unilateral neck flexion

Note***Complex innervation of brachiocephalicus m. indicates that the muscle resulted from fusion of various muscles from evolution

Pectoral muscles

1. Superficial



2. Deep (Ascending)

1. First two sternebrae and associated costal cartilages
2. All sternebrae

1. Crest of major tubercle of humerus
2. Greater and lesser tubercles of humerus

1. Cranial pectoral n.

2. Caudal pectoral n.

Adduction of limb; helps to draw limb backwards, or pull trunk forward

Cat Differences

  • Cleidobrachialis m. is broader, and has tendinous attachment to ulna

  • Latissimus dorsi m. is partially fused to superficial pectoral in the axillary region

Why does the clavicle of the cat (but not the dog) have radiographic significance? The clavicle of the cat is well-developed and serves to stabilize the shoulder for climbing, whereas the absence of a clavicle in the dog allows for efficient running. On a lateral radiograph, the clavicle of a cat may be mistaken for a bone in the esophagus, so two radiographic views must be taken.

Muscles of the Neck



Origin (or Attachments)


N. Supply


Sphincter colli superficialis


1. Facial

2. Cervical

Twitches skin over nape of neck

Sphincter colli profundus

Only in carnivores

Cutaneous trunci

Maybe derivative of deep pectoral m.

Lateral thoracic n.

Twitches skin over body


1. Occipital

2. Mastoid (deeper)

1. Manubrium of sternum

2. “ “

1. Nuchal line of occipital bone

2. Mastoid part of the skull

Accessory n. (CN XI)

Flexes the neck when acting bilaterally; helps to turn the head to one side

Note***External jugular vein runs on the lateral surface of the sterno-occipital part of the sternocephalicus m.


1. Sternohyoideus

2. Sternothyroideus

1. Manubrium of sternum

2. “ “

1. Basihyoid bone of hyoid apparatus

2. Lateral surface of thyroid cartilage

Draw the larynx and tongue caudally (aids in swallowing)

Longus capitis

Longus colli

“V”-shaped attachments points on vertebral bodies

Carotid Sheath

  • Made up of deep fascia, which is continuous with the fascia of the thorax

    • Any infection of the carotid sheath can potentially cause infection in the thorax

  • Envelops 5 structures:

    • Common carotid artery

    • Internal jugular vein

    • Vagosympathetic trunk

    • Tracheal lymph duct

    • Recurrent laryngeal n.

Cat differences

  • Nuchal ligament absent

Intrinsic Muscles of the Thoracic Limb

(Muscles that confine their attachments to the bones of the thoracic limb)



Origin (or Attachments)


N. Supply


Shoulder muscles:


Supraspinous fossa, part of scapular spine, scapular neck

Greater tubercle of the humerus

Suprascapular n.

Extension of the shoulder


Infraspinous fossa. scapular spine

Lateral aspect of the greater tubercle of the humerus

Suprascapular n.

Mainly flexes the shoulder; slight abduction of the limb

Clinical note***The infraspinatus m. tendon of insertion has a bursa associated with it. Bursitis of this structure may results in lameness of the shoulder

Teres minor

Mainly from infraglenoid tubercle

Tricipital line of humerus

Axillary n.

Flexes shoulder

Note***When caudal surgical approach to shoulder is attempted, teres minor m. must be reflected from joint capsule to which it closely attaches


1. Spinous

2. Acromial

1. Spine of the scapula

2. Acromion of scapula

1. Deltoid tuberosity

2. “ “

Axillary n.

Mainly flexes shoulder; slight abduction of limb

Clinical note***The deltoid m. does not have tendinous origin, but muscle fibers attach directly to acromion. In order to access shoulder joint, a surgeon cannot simply reflect the muscle, but must perform acromiol osteotomy. Closure would require wiring of the acromial process back on the scapular spine


Subscapular fossa (medial aspect) of scapular

Lesser tubercle of humerus

Subscapular and axillary n.s

Minor adduction of limb; aid in flexion/extension

Teres Major

Caudal angle of scapula

Teres tubercle

Axillary n.

Flexes shoulder

Clinical note***Phylogenetically, teres major m. is part of latissimus dorsi m.


Coracoid process of scapula

Near teres tubercule

Musculocutaneous n.

Vestigal muscle; may extend shoulder

Brachial muscles:

Triceps Brachii

1. Long head

2. Medial “

3. Lateral “

4. Accessory “

1. Caudal border of scapula

2. Proximal medial shaft of humerus (near teres tubercle)

3. Tricipital line

4. Neck of humerus


Radial n.

Flexes shoulder; extends elbow; crucial in supporting the weight of the animal at the elbow

Tensor fascia antebrachii

Latissimus dorsi


Radial n.

Extend Elbow

Biceps brachii

Supraglenoid tubercle

Ulnar and radial tuberosities

Musculocutaneous n.

Strong flexion of the elbow; weak extension of the shoulder


Caudal aspect and neck of the humerus

Ulnar and radial tuberosities

Musculocutaneous n.

Flex elbow


Lateral epicondyle and its crest; partly median epicondyle

Proximolateral aspect of the ulna

Radial n.

Extend elbow

Muscles of the carpus and digits:

Note***Most of the antebrachial muscles have tendon sheaths in the carpal region

Note***The extensors of the carpus and digits are on the craniolateral aspect of the antebrachium

Note***The brachioradialis m. has a 35% occurrence in the dog. It is always in the cat. It is an insignificant muscle located in the superficial fascia


Proximal aspect of the lateral epicondylar crest of the humerus

Distal radius

Radial n.

Aids in supination

Extensor carpi radialis (ECR)

Cephalic vein lies on this m.

Lateral epicondylar crest of the humerus

Dorsal aspect of metacarpal II and III

Radial n.

Extends carpus; weak flexion of the elbow

Common digital extensor (CDE)

4 distal tendons

Lateral epicondyle of the humerus

Ungual crest of 3rd phalanx of digist II-V

Radial n.

Extends carpus and digits

Lateral digital extensor (LDE)

3 tendons join w/ those of CDE

Lateral collateral ligament of elbow; partly from proximal radius

Ungual crest of distal phalanges of digist III-V

Radial n.

Extends lateral digits (III, IV, and V)

Extensor carpi ulnaris

(Ulnaris lateralis)

2 distal tendons

Lateral epicondyle of the humerus

Proximolateral aspect of metacarpal V and accessory carpal bone

Radial n.

May extend the carpus; may flex the carpus

Abductor pollicis longus

Lateral surface of radius and ulna

Proximomedial aspext of metacarpal I

Radial n.

Abducts digit I; extends carpus; may supinate paw


Lateral epicondyle of the humerus

Cranial surface of the radius

Radial n.

Supinates paw

Note***The flexors of the carpus and digits are located on the caudomedial aspect of the antebrachium

Pronator quadratus

Interosseus surfaces on medial aspect of radius and ulna

Median n.

Not much (weak pronation)

Deep digital flexor (DDF)

1. Ulnar head

2. Humeral head

3. Radial head

1. Median epicondyle of humerus

2. Caudal surface of ulna

3. Medial surface of radius

Distal phalanges of all digits (I-V)

Ulnar and Median nerves

Flexes the carpus and digits

Note***If either the Ulnar or Median nerve (not both) is damaged, the DDF will still function

Flexor carpi ulnaris

1. Humeral head

2. Ulnar head

1. Medial epicondyle of the humerus
2. Proximocaudal aspect of the ulna

Tendons from both heads unite to attach to accessory carpal bone

Ulnar n.

Flexes carpus

Superficial digital flexor (SDF)

4 distal tendons

Median epicondyle of the humerus

Palmar aspect of middle phalanx of digits II-V

Median n.

Flexes carpus and digits II-V

Note***Each tendon of the SDF divides to permit the tendons of the DDF to pass through. This arrangement is called a manica flexoria

Flexor carpi radialis

Medial epicondyle of the humerus

Proximolateral aspect of metacarpals II and III

Median n.

Flexes carpus

Pronator teres

Medial epicondyle of the humerus

Cranial surface of the radius

Median n.

Pronates paw

Note***There are 4 interosseus muscles of forepaw (digits II-V)

Interosseus muscles of forpaw

Proximopalmar aspects of metacarpals II-V

Each muscle tendon splits into 2 branches, eventually joining the CDE tendons

Ulnar n.

Flexes metacarpo-phalangeal joints

Cat Differences

  • On the scapula, the hamate and suprahamate are processes of the acromion

  • Biceps brachii m. attaches only to radius

  • On the humerus, there is a supracondylar foramen

  • Brachioradialis m. is well-defined, while absent in dog

  • Complete claw-retention mechanism…HOW?

    • Dorsal elastic ligaments in the car are stronger. Also, the articular facets between P2 and P3 in the cat are sloped so that when P3 is retrached, it is displaced to the lateral surface of P2.

  • Median n. and brachial artery pass through the supracondyloid foramen on cat

Muscles of the Pelvic Limb



Origin (or Attachments)


N. Supply


Note***There are no “extrinsic” muscles of the pelvic limb because the pelvic limb articulates with the axial skeleton via attachment of the os-coxae (hipbone) to vertebrae

Tensor fascia latae

1. Cranial

2. Caudal

Tuber coxae, aponeurosis of middle gluteus m.

Lateral femoral fascia

Cranial gluteal n.

Tense lateral femoral fascia; flex hip; extend stifle (indirectly)

Superficial gluteus

Sacral tuberosity of the ilium via deep fascia, lateral sacrum, 1st caudal vertebrae, cranial sacrotuberous ligament

3rd trochanter of the femur

Caudal gluteal n.

Extends hip joint

Middle gluteus

Lateral gluteal surgace of ilium

Greater trochanter

Cranial gluteal n.; sometimes caudal gluteal n.

Extends hip joint


Fusiform m.

Last sacral and 1st caudal vertebrae

Greater trochanter

Caudal gluteal n.

Extends hip joint

Deep gluteus

Lateral shaft of ilium

Greater trochanter

Cranial gluteal n.

Extends hip joint

Internal obturator

“fire hydrant” m.

Intrapelvic borders surrounding obturator foramen

Trochanteric fossa

Sciatic n.

Abducts hip joint


Tendon of the internal obturator m.

Sciatic n.

Abducts hip

Quadratus femoris

Ventral surface of ischium

Ventral to trochanteric fossa, caudal proximal femur

Sciatic n.

Extends hip; weak abduction of hip

Biceps femoris

1. Cranial

2. Middle

3. Caudal

Ischial tuberosity, distal part of sacrotuberous ligament

1. Patella

2. Tibial crest

3. Tuber calcaneous

Sciatic n.; caudal gluteal n.

Extends hip, stifle, and hock; flexes stifle

Abductor cruris caudalis (caudal crural abductor)

Sacrotuberous ligament

Distal lateral crural fascia

Sciatic n.

Abducts limb


Ischial tuberosity

Medial aspect of tibial crest, tuber calcaneus

Sciatic n.

Extends hip and hock; flexes stifle


1. Cranial belly

2. Caudal belly

Ventral aspect of ischiatic tuberosity and arch

1. Distal aspect of femur

2. Medial condyle of tibia

Sciatic n.

Extends hip joint; only caudal belly flexes the stifle

Clinical note***Do not use the semimem. and semiten. for IM injections because the sciatic nerve could be damaged. Better to use the middle gluteus or epaxial muscles

Quadriceps femoris

Rectus femoris m., lateral and intermediate vastus lateralis m.

Patella, patellar ligament attached to tibial tuberosity

Femoral n.

Bearing weight on pelvic limb; flexes hip; extends stifle


1. Cranial

2. Caudal

Iliac crest

1. Patella

2. Medial tibial crest

Femoral n.

Flexes hip; cranial part extends stifle; caudal part flexes stifle

Muscles innervated by the obturator nerve:


Prepubic tendon

Medial lip of femur

Obturator n.

Adducts limb

Clinical note***Craniomedial to the pectineus m. is the inguinal canal, which is palpated to examine an inguinal hernia. Cutting this muscle may temporarily relieve pain


1. Magnus et brevis

2. Longus

Pelvic symphysis via symphyseal tendon

1. Lateral lip of femur

2. Caudal femur ventral to inter-trochanteric ridge

Obturator n.

Adducts limb; may extend hip


Pelvic symphysis via symphyseal tendon

Cranial tendon to medial aspect of tibial crest, caudal tendon to tuber calcis

Obturator n.

Adducts limb; weak stifle extension; weak hock extension

External obturator

Outer margins of obturator foramen, ventral aspect of hip bone

Trochanteric fossa

Obturator n.

Adducts limb

Crural muscles (those related to the tibia and fibula) of the pelvic limb:

Cranial tibial

Lateral proximal tibia, tibial crest, extensor sulcus

Metatarsals I and II, proximo-plantar aspect

Peroneal n.

Flexes tarsus; supination of limb; no action on stifle

Long digital extensor

Extensor fossa of femur

P3 Ungual crest of digits II-V

Peroneal n.

Flexes hock; extends digits

Peroneus longus (fibularis longus)

Lateral condyle of tibia, proximal aspect of fibula

Plantar aspect of 4th tarsal bone, proximo-plantar aspect of all metatarsal bones

Peroneal n.

Flexes tarsus, pronation of limb

Lateral digital extensor


Peroneal n.


Peroneus brevis

Peroneal n.

Flexes tarsal joint

Muscles innervated by the tibial nerve:


1. Lateral head

2. Medial head

1. Lateral supracondylar tuberosity

2. Medial supracondylar tuberasity

Tuber calcaneus

Tibial n.

Flexes stifle; extends hock

Note***Each head of the gastrocnemius m. has a sesamoid bone at its origin, called a fabella, which both form a synovial joint with the femoral condyles

Note***In the cat, the gastrocnemius m. and the soleus m. are together called the “triceps surae”

Superficial digital flexor (SDF)

Lateral supracondylar tuberosity, lateral head of gastrocnemius m.

Tuber calcis, terminates in 4 tendons of P2 of all digits

Tibial n.

Flexes stifle and all digits; extends tarsal joint

Note***There is a synovial bursa under the SDF m. tendon over the calcanean tuberosity. This bursa can be inflamed and enlarged, a condition called “capped hock”

Deep digital flexor (DDF)

1. Lateral head

2. Medial head

1. Caudal fibula, caudal-lateral tibia

1. Proximo-caudal tibia

Common tendon of talus, which terminates at plantar aspect of P3 of digits II-V

Tibial n.

1.Extends tarsal joint; flexes digits

2. Nothing

Note***The DDF m. has 2 heads in carnivores and 3 heads in ungulates


Popliteal fossa of femur

Proximo-caudal tibia

Tibial n.

Flexes stifle, pronation of limb

5 Muscles of the Common Calcanean Tendon

  • Biceps femoris m.

  • Semitendinosus m.

  • Gastrocnemius m.

  • Superficial digital flexor (SDF) m.

  • Gracilis m.

  • Soleus m. (only cat)

Cat Differences

  • No sacrotuberous ligament

  • Sartorius m. is not divided into 2 bellies

  • Caudofemoralis m. (adductor cruris cranialis m.) only in cat

Muscles of Thorax and Abdomen

(Derived from hypomeres of somites and innervated by ventral branches of the spinal nerves)



Origin (or Attachments)


N. Supply


Muscles of the thoracic wall:


1. Dorsal scalenus (Dorsal and Ventral parts)

2. Middle scalenus

3. Ventral

Serratus ventralis cervicis

Serratus ventralis thoracis

Serratus dorsalis cranialis

Serratus dorsalis caudalis

Thoracolumbar fascia

Proximo-caudal margin of ribs 11-13

Intercostal n.s

Aids in expiration

External intercostals

Fiber direction is caudoventral (caudal edge of one rib to cranial end of succeeding rib)

Intercostal n.s

Aid in inspiration

Internal intercostals

Fiber direction is cranioventral (cranial edge of one rib to caudal end of preceding rib)

Intercostal n.s

Aid in expiration

Rectus thoracis

1st rib

Ventral ends of ribs 2-4

Intercostal n.s

Aids in inspiration

Muscles of the abdominal wall:

Note***Only in carnivores, the superficial fascia of the trunk is neither attached to the spinous processes nor the linea alba, but forms a continuous sheet of connective tissue from one side of the body to the other. This is why a wet dog can move their trunk skin extensively to dry themselves

External abdominal oblique

Lateral aspect of ribs, thoracolumbar fascia from T-processes of lumbar vertebrae

Wide aponeurosis to linea alba, prepubic tendon, and shaft of ileum

Ventral branches of thoracic and lumbar n.s

Compresses abdomen; aids in expiration

Internal abdominal oblique

Tuber coxae, thoracolumbar fascia

Costal arch, last rib, linea alba, prepubic tendon

Ventral branches of last thoracic n.s, 1st lumbar n.s

Compresses abdomen; aids in expiration


Transverse abdominis

Tuber coxae, lumbar T-processes, costal cartilarges

Linea alba, prepubic tendon

Ventral branches of last thoracic and lumbar n.s

Compresses abdomen; aids in expiration

Rectus abdominis

Ventral aspect of sternum

Prepubic tendon

Thoracic and few lumbar n.s

Compresses abdomen; aids in expiration

Epaxial Muscles

(Derived from epimeres, express MYF5 protein during development, innervated by dorsal branches of spinal nerves)



Origin (or Attachments)


N. Supply


Muscles of the Transversospinalis system:


Semispinalis capitis

1. Biventor 2. Complexus

Parts of the Longissimus system (longest muscle system in the body):

Longissimus capitis

Attaches to the head

Longissimus cervicis

Attaches to the cervical vertebrae (has 3-4 fascicles)

Longissimus thoracis

Longissimus lumborum

Parts of the Iliocostalis system:

Iliocostalis thoracis

Iliocostalis lumborum

Note***In the lumbar region, the longissimus lumborum m. and iliocostalis lumborum m. are fused, giving rise to a strong erector spinae m. (in humans)

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