1.9 Intrinsic Muscle of the Thoracic Limb: Muscles of the Forepaw

Muscles of the Forepaw

Interflexorius/ flexor digitorium brevis manus

Lumbricales

Abductor digit I (pollicis) brevis

Flexor digiti I brevis

Adductor digiti I /adductor pollicis

Adductor digiti V

Abductor digiti V

Flexor digiti V

Adductor digiti II

Interosseous/ Interossei

name the muscles of the forepaw (10)

Interflexorius/ flexor digitorium brevis manus

• this muscle originates from a fascial sheet from flexor digitorium profundus muscle (humeral, medial, and lateral head) in the distal one quarter of the antebrachium.

• Origin: lateral superficial belly of the humeral head of the DDF

• Insertion: tendon of the SDF for digits 3-4

• Action: to flex the forepaw

• Innervation: Median nerve

Lumbricales

• three-thin (1st, 2nd, 3rd) muscles originate from the tendon of flexor digitorium profundus muscle.

• superficial to the flexor brevis profundus

• muscle fibers passes parallel to the long axis of the metacarpals

• between the tendon of deep digital flexor muscle

• muscle belly of lumbricales inserts to digits 3-4 (largest), between 4-5 (smaller)

• Origin: 1st-DDF tendonto the 2nd-3rd digits, 2nd-3rd & 4th digit, 3rd-4th & 5th digit

• Insertion: 1st - 3rd digit, 2nd - 4th digit, 3rd - 5th digit

• Action: to flex the MCP joint

• Innervation: Ulnar nerve

Abductor digit I (pollicis) brevis

• short, cylindrical muscle originates from the flexor retinaculum

• proximal to the origin of the flexor brevis profundus muscle

• minimal mobility

• lies superficial to flexor digit 1

• inserts on the 1st metacarpal

• vestigial because the 1st digit is the hallux

• has no bone insertion

• Origin: flexor retinaculum

• Insertion: ligamentous tissue at the metacarpophalangeal joint of the digit 1

• Action: to abduct and flex the 1st digit

• Innervation Ulnar nerve

Flexor digiti I brevis

• short, thick muscle with muscle fibers traveling parallel to the metacarpals

• Origin: radiate carpal ligament

• Insertion: sesamoid bone or the proximal phalanx

• Action: to flex the digit 1

• Innervation: Ulnar nerve

Adductor digiti I /adductor pollicis

• short, fan shaped muscle that is wide at origin and tapers at its insertion

• superficial to the flexor digiti 1 brevis

• Origin: between the special flexor and interosseous muscle

• Insertion: lateral surface of the proximal phalanx of digit 1

• Action: to adduct and flex the 1st digit

• Innervation: Ulnar nerve

Interosseous

• A muscle of the manus arising from the proximal palmar surface of the metacarpal bones.

• it extends distally and splits into two tendons

• Origin: metacarpal 2-5

• Insertion: unite with the common digital extensor tendon

• Action: to flex the MCP joint

• Innervation: Ulnar nerve

interosseous membrane of forearm

• connects radius and ulna as a membrane only in carnivores

• a thick syndesmosis seen in between the diaphysis/shaft of the radius and ulna

• The membrane is situated both proximal and distal to the interosseous ligaments and attaches apposed interosseous crests of the radius and ulna

interosseous ligament of forearm

• a short, thick ligament connects the radius and ulna in the proximal half of interosseous space in carnivores, lateral to interosseous membrane of forearm

Adductor digiti V

Abductor digiti V

Flexor digiti V

Adductor digiti II

name the special muscles if the digit 5 and digit 2

Adductor digiti V

• flat, fan-shaped muscle with slight aponeurosis on the proximal two-thirds of its palmar surface.

• axial

• Origin: radiate carpal ligament

• Insertion: metacarpal 5 and proximal phalanx of the digit 5

• Action: to adduct the 5th digit

• Innervation: Ulnar nerve

Abductor digiti V

• small, flat muscle that arises from the distal aspect of the pisiform

• abaxial

• muscle fibers passes obliquely and laterally from the pisiform to the lateral manus

• the muscle produces a thin transparent aponeurosis at the proximal quarter of deep metacarpal which forces distally and inserts at the lateral base of the proximal phalanges of digit v

• Origin: accessory carpal bone

• Insertion: tendon of flexor digit 5

• Action: to abduct the 5ht digit

• Innervation: Ulnar nerve

Flexor digiti V

• small muscle that lies distal to the origin of abductor digiti V muscle and travels laterally over the flexor digitorium brevis digiti IV muscle

• muscle arises from the flexor retinaculum of the pisiform

• becomes tendonous and fuses with the tendon of the abductor digit V muscle

• Origin: ligament from the accessory carpal bone to the metacarpal 4

• Insertion: joins the abductor digit 5

• Action: to flex the digit 5

• Innervation Ulnar nerve

Adductor digiti II

• relatively thick band of muscle lying on the palmar side of carpometacarpal joint.

• Origin: radiate carpal ligament

• Insertion: base of the proximal phalanx of digit 2

• Action: to adduct the digit 2

• Innervation: Ulnar nerve