Thoracic Limbs

Vestigial paw pads

• chestnut: carpal

• ergot: metacarpal

Glenohumeral/shoulder joint

• ball & socket joint

• medial + lateral glenohumeral ligaments

• flexes & extends shoulder but can move any direction

• luxation rare, stabilized by muscles

• caudal flexor surface

Cubital/elbow joint

• compound hinge joint

• only involved in flexion & extension

• lateral/ulnar + medial/radial collateral ligaments

• interosseous ligament uniting radius & ulna

• luxation uncommon due to anconeal process in olecranon fossa

• cranial flexor surface

Knee

• carpal joint

• palmar flexor surface

Fetlock joint

• metacarpophalangeal joint

• aka ankle

• palmar flexor surface

Pastern joint

• proximal interphalangeal joint

• palmar flexor surface

Coffin joint

• distal interphalangeal joint

• palmar flexor surface

Scapular fossae

• infraspinous - ventral to spine

• supraspinous - dorsal to spine

• subscapular - medial aspect

Tuber spinae

• projection off of scapular spine

• caudal/ventral acromion process in dogs

Glenoid cavity

• the articulation of the scapula & humerus to form the glenohumeral joint

• supraglenoid tubercle dorsally/cranially

Coracoid process

• medial projection of the supraglenoid tubercle

Serrated face

• medial surface of the scapula where serratus ventralis sling attaches

Humeral tubercles

• greater - lateral

• lesser - medial

• both have cranial & caudal parts

Intermediate tubercle

• middle tubercle of the humerus

• inter-tubercular groove

Humeral tuberosities

• deltoid - lateral

• teres major - medial

Humeral epicondyles

• lateral - origin for carpal & digital extensors, capitulum attached & articulates w/radius

• medial (larger) - origin for carpal & digital flexors, trochlea attached & atriculates w/radius & ulna

  • supratrochlear foramen in dogs, distomedial supracondylar foramen in cats (brachial a. + median n.)

Humeral fossae

• radial - cranial

• olecranon - caudal

Olecranon tuberosity

• point of the elbow

Ulna

• vestigial structure fused to radius, not fully developed

  • antebrachial interosseous space between radius & ulna

• proximal olecranon + tuber, anconeal process, & trochlear notch

Radius

• principle weight-bearing bone of the forearm

• distal trochlea w/styloid process

Styloid process

• lateral from ulna, medial from radius

Radial grooves

• common digital extensor

• extensor carpi radialis

• extensor carpi obliquus/abductor pollicis longus

Radius & ulna relationship

• radius cranial proximally & medial distally

Proximal carpal bones

• radial carpal

• intermedial carpal

• ulnar carpal

• accessory carpal (lateral)

Distal carpal bones

• 1st - 4th carpal

• ± 1st carpal

Metacarpal bone II

• common name: medial splint bone

Metacarpal bone III

• common name: cannon bone

• metacarpal tuberosity proximal

Metacarpal bone IV

• common name: lateral splint bone

Sagittal ridge of metacarpal bones

• proximal end base, distal end head

Proximal sesamoid bone

• located at fetlock joint/head of the metacarpals

Distal sesamoid bone

• navicular bone w/podotrochlear bursa

• located between middle and distal phalanx

Phalanges

• proximal phalanx/long pastern bone/P1

  • base, body, head

• middle phalanx/short pastern bone/P2

  • base, body, head

• distal phalanx/coffin bone/P3

  • base, extensor process, ungual crest, ungual process

• digit 1 missing middle phalanx

Extensor process

• insertion of common digital extensor

Palmar process

• attachment of hoof cartilage to distal phalanx

Parietal sulcus

• pathway for blood vessels in the distal phalanx

Solar canal

• contains anastomosis of lateral and medial digital arteries

Flexor surface

• site of insertion for deep digital flexor tendon in the hoof

Thoracic girdle

• attaches limb to trunk

• scapula + clavicle (vestigial cartilage)

Cervical spinal nerve

• innervates rhomboideus cervicis

Long thoracic nerve

• innervates serratus ventralis cervicis & thoracis

Lateral thoracic nerve

• innervates cutaneous trunci

Thoracodorsal nerve

• innervates latissimus dorsi - flex shoulder

CN XI

• innervates:

  • trapezius (cervicis & thoracis)

  • brachiocephalicus

  • omotransversarius

    • fused to brachiocephalicus

Cranial & caudal pectoral nerves

• innervates extrinsic pectoral muscles

  • descending, transverse, deep

  • subclavius

• adduct limbs

Musculocutaneous & median nerve

• fused proximally

• communication branch

Subscapular nerve

• innervates:

  • supraspinatus (lateral) - extends + stabilizes shoulder

  • infraspinatus (lateral) - abducts shoulder

  • subscapularis (medial) - adducts shoulder

Axillary nerve

• innervates:

  • deltoideus (lateral)

  • teres minor (lateral)

  • teres major (medial) - rotates arm medially

• flex shoulder

Coracobrachialis

• medial scapular muscle

• innervated by musculocutaneous n.

• extends shoulder

Caudal muscles of brachium

• muscles:

  • triceps brachii (long, lateral, medial, accessory)

    • long head flexes shoulder

  • tensor fasciae antibrachii

  • anconeus

• innervated by radial n.

• extend elbow

Cranial muscles of brachium

• muscles:

  • brachialis

  • biceps brachii - extends shoulder

• innervation from musculocutaneous nerve

• flex elbow

Biceps brachii & triceps brachii long head

• span 2 joints, do not attach to humerus

• have opposite effects on the shoulder joint as they do on the elbow joint

Lacertus fibrosus

• central tendon of biceps

• inserts on extensor carpi radialis

• locks limb

Craniolateral muscles of antebrachium

• muscles:

  • extensor carpi radialis (largest) & obliquus

  • common & lateral digital extensors

  • ulnaris lateralis

  • abductor pollicis longus - abducts thumb

  • supinator - supinates paw

• innervation from radial n.

• extend carpus & digit(s)

Caudomedial muscles of antebrachium

• muscles:

  • deep digital flexor (ulnar, radial, humeral head)

  • flexor carpi radialis

  • flexor carpi ulnaris (ulnar & humeral heads)

  • superficial digital flexor

  • pronator teres & quadratus - pronate paw

• innervation from median & ulnar n.

• flex carpus & digit(s)

Palmar muscles of carpus

• muscles:

  • interosseus (aka suspensory ligament)

• innervation from median & ulnar n.

• flex metacarpophalangeal joints

Accessory ligament of superficial digital flexor

• proximal check ligament

Accessory ligament of deep digital flexor

• distal check ligament

Synovial joint

• joint cavity

• joint capsule

  • outer fibrous layer - thicker, forms ligaments

  • inner synovial membrane - vascular connective tissue, produces synovial fluid

• synovial fluid

• articular/hyaline cartilage - thicker when more weight-bearing

Compound joint

• individual synovial compartments w/in a common fibrous capsule

• antebrachiocarpal + midcarpal + carpometacarpal joint

  • mobility decreases distally

  • midcarpal + carpometacarpal communicate

Retinacula

• bands of fascia holding tendons in place

• flexor + extensor

Synovial tendon sheaths

• a bursa that surrounds a tendon to improve glide

• flexor carpi ulnaris + ulnaris lateralis

Annular ligaments

• fascia holding tendons in place

  • palmar + proximal digital + distal digital

Digital extensors

• common + lateral

• insert on extensor process of P3

• extensor branch of interosseus m. fuses to common

Digital flexors

• deep: inserts on flexor process of P3

• superficial: inserts on distal P1, proximal P2, & manica flexoria

• superficial inserts proximally to deep, deep passes through manica flexoria

Epidermal hoof structures

• insensitive

  • periople/perioplic groove

  • hoof wall

  • coronary groove

  • laminae

  • spine of frog

Dermal hoof structures

• sensitive

  • laminar corium (walls + bars)

  • papillary corium (perioplic corium, coronary corium, corium of frog, corium of sole)

Coronary band

• perioplic dermis

• coronary dermis

• coronary cushion

Venous plexuses of hoof

• coronary + dorsal + palmar

• drain into digital vein for venous return

Concussive mechanism of hoof

• absorbs concussive force

• pumps blood from foot into digital vein

Passive stay apparatus

• prevents flexion of shoulder + elbow

• prevents over-extension of carpus + fetlock

  • suspensory + sesamoidean ligament

Ruminant metacarpal bones

• large: fused III + IV

  • equivalent of cannon bone in horses

• small: V (vestigial & lateral)

Ruminant digits

• medial: 3rd

• lateral: 4th

• medial dewclaw: 2nd

• lateral dewclaw: 5th

Interdigital gland

• gland between the digits of ovine species used for marking

Ruminant hoof differences

• bulb instead of frog

• only primary laminae, no secondary

Major arterial branches

• axillary

• brachial

• median

• medial palmar (after carpal canal)

• medial & lateral digital

• arcus terminalis (solar canal)

Axillary a.

• suprascapular

• subscapular (order of branches flipped in dog)

  • caudal circumflex humeral

  • thoracodorsal

• cranial circumflex humeral

  • cranial & caudal circumflex form a ring

Brachial a.

• deep brachial

• bicipital

• collateral ulnar

• superficial brachial

• transverse cubital

• common interosseus

  • cranial + caudal

Rete carpus dorsale

• formed from transverse cubital + cranial interosseus

• weblike network of arteries on carpal dorsum

• branches into medial + lateral dorsal metacarpal (small & deep arteries)

Median a.

• deep antebrachial(s) (→ caudomedial mm.)

• proximal radial (→ carpal joint)

• palmar branch (fuses w/collateral ulnar & forms lateral palmar)

  • contributes to deep palmar arch

  • fuses w/lateral digital

• radial branch (only branch of concern in dog)

  • contributes to deep palmar arch & gives rise to medial + lateral palmar metacarpal

Median palmar a.

• principle blood flow to the digit

• median + lateral digital

  • dorsal + palmar → P1-3

  • branch to digital cushion

Brachial plexus

• ventral branches of spinal nerves C6-8 + T1-2

• separates into individual nerves after intervertebral foramen

Median nerve branches

• medial + lateral palmar → medial + lateral digital @ fetlock

  • give rise to dorsal branches distal to fetlock that terminate @ corium

• communicating branch on SDF

Ulnar nerve branches

• dorsal branch

• palmar branch that fuses w/lateral palmar branch of the median n.

  • deep branch of lateral palmar → medial + lateral palmar metacarpal

Cutaneous antebrachial nerves

• cranial from axillary

• caudal from ulnar

• medial from musculocutaneous

  • last branch before median n. splits off

• lateral from radial

Superficial pectorals

• descending + transverse

• adduct limb

• innervated by cranial pectoral nerve

Deep pectoral

• adducts limb

• innervated by caudal pectoral nerve

Brachiocephalicus

• cleidocephalicus

  • cleidocervicalis + cleidomastoideus

• cleidobrachialis

• draw limb cranially

• innervated by accessory nerve + cervical spinal nerves

Omotransversarius

• draws limb cranially

• innervated by accessory nerve + cervical spinal nerves

Trapezius

• cervical + thoracic

• elevates limb

• innervated by accessory nerve

Latissimus dorsi

• draws limb caudally

• innervated by thoracodorsal nerve

Serratus ventralis

• cervicis + thoracis

• supports trunk + depresses scapula

• innervated by long thoracic nerve + cervical/thoracic spinal nerves

Rhomboideus

• capitis + cervicis + thoracis

• elevate trunk + draw scapula toward trunk

• innervated by cranial/thoracic spinal nerves

Sternocephalicus

• sternomastoideus + sterno-occipitalis

• moves head side to side (unilateral) + flexes neck (bilateral)

• innervated by accessory nerve + cervical spinal nerves

• technically not extrinsic

Cutaneous trunci

• thin muscle sheet covering abdomen and thorax walls

• innervated by lateral thoracic nerve

• twitch muscle

Arteries

• thick/rigid wall

• hold pressure, not volume

• carry blood away from heart (typically oxygenated)

Anastomoses

• alternative interarterial pathways for blood if a more direct route is blocked

Veins

• thin walls, collapsed appearance

• hold large volumes, not pressure

• valves ensure unidirectional blood flow

• carry blood to the heart (typically deoxygenated)

Venous pattern

• axillary

• brachial

• median

  • named with location of arteries

• cephalic (palmar paw)

• accessory cephalic (dorsal paw)

Lymphatic system

• vessels that return interstitial fluid to the bloodstream via venous system

• scattered aggregations of lymph tissue (nodes)

Lymph nodes of thoracic limb

• superficial cervical: deep face of omotransversarius, drains caudal head, lateral neck, & thoracic limb

• axillary: medial shoulder, drains deep thoracic limb, thoracic wall, & cranial mammary glands

  • ± accessory axillary: same areas as axillary