Muscle Anatomy of the Pelvic Limb and Tail

m. psoas minor

Function: Steepens pelvis by flexing the lumbosacral joint or flexes lumbar vertebral column; Innervation: Lateral branches of ventral lumbar nerves (L1-L4 or L5); Thin and runs ventromedially.

m. psoas major

Function: Draws pelvic limb cranially (hip flexor); fixes or flexes vertebral column; Innervation: Branches of rami ventrales of lumbar nerves; Lies between quadratus lumborum and psoas minor.

m. quadratus lumborum

Function: Flexes and stabilizes lumbar vertebral column; Innervation: Ventral branches of lumbar spinal nerves; Lies ventral to thoracic/lumbar vertebrae and last two ribs.

m. tensor fasciae latae

Function: Flexes hip, extends stifle via fascia lata; Innervation: Cranial gluteal nerve.

m. gluteus superficialis

Function: Extends hip, abducts limb; Innervation: Caudal gluteal nerve.

m. gluteus medius

Function: Extends hip, abducts limb; Innervation: Cranial gluteal nerve; Largest gluteal muscle.

m. gluteus profundus

Function: Abduction and medial rotation of thigh; Innervation: Cranial gluteal nerve; Deepest gluteal muscle.

m. piriformis

Function: Extends hip, abducts limb; Innervation: Caudal gluteal nerve.

m. articularis coxae

Function: Tenses capsule of hip joint; Innervation: Femoral nerve; Smallest muscle of the hip.

m. biceps femoris

Function: Extends hip, stifle, hock; flexes stifle when not bearing weight; Innervation: Sciatic nerve; Largest muscle of the thigh.

m. semitendinosus

Function: Extends hip and hock, flexes stifle; Innervation: Sciatic nerve.

m. semimembranosus

Function: Extends hip and stifle (partially flexes stifle); Innervation: Sciatic nerve.

m. sartorius

Function: Flexes hip; cranial belly extends stifle, caudal belly flexes stifle; Innervation: Femoral nerve; Two bellies in dogs: cranial and caudal.

m. gracilis

Function: Adducts limb, extends hip, stifle, and hock; Innervation: Obturator nerve.

m. adductor magnus et brevis

Function: Adducts limb, extends hip; Innervation: Obturator nerve.

m. adductor longus

Function: Same as above (adduction, hip extension); Innervation: Obturator nerve.

m. pectineus

Function: Adduction of the limb; Innervation: Obturator nerve.

m. quadriceps femoris

Function: Extends stifle (rectus also flexes hip); Innervation: Femoral nerve; Main extensor of the stifle; essential for weight-bearing.

m. iliopsoas

Function: Flexes hip; Innervation: Femoral nerve and lumbar spinal nerves; fused m. iliacus + m. psoas major.

m. tibialis cranialis

Function: Flexes the tarsus and rotates the paw laterally (supination); Innervation: N. fibularis; Superficial, flattened muscle on cranial tibia.

m. extensor digitorum longus

Function: Extends the digits and flexes the tarsus; Innervation: N. fibularis; Spindle-shaped, 2-2.5 cm thick; between tibialis cranialis and fibularis longus.

extensor digiti I (hallucis) longus

Function: Extends digit II; may extend digit I; Innervation: N. fibularis profundus; Small elliptical band covered by extensor digitorum longus and fibularis longus.

m. extensor digitorum lateralis

Function: Extends digits III-V; Innervation: N. fibularis; Lies beside extensor digitorum longus.

m. fibularis (peroneus) longus

Function: Pronates hindpaw (rotates plantar surface laterally), flexes tarsus; Innervation: N. fibularis; Short-bellied; on lateral surface of proximal crus.

m. gastrocnemius (medial & lateral heads)

Function: Extends tarsus, flexes stifle; Innervation: N. tibialis; Forms caudal bulge of the leg; largest caudal muscle.

m. soleus

Function: Weak extensor of tarsus; Innervation: N. tibialis; Vestigial or absent in canines.

m. flexor digitorum superficialis

Function: Extends tarsus and flexes digits II-V; Innervation: N. tibialis; Shares Achilles tendon with gastrocnemius.

m. flexor digitorum profundus

Function: Flexes all digits; Innervation: N. tibialis; Composed of three heads: lateral, medial, tibialis caudalis.

m. popliteus

Function: Rotates leg medially; Innervation: N. tibialis; Fan-shaped muscle at back of knee.

m. interflexorius

Function: Flexion of the forepaw; Innervation: N. medianus; Originates from palmar tendinous sheet of the lateral superficial belly of m. flexor digitorum profundus.

m. flexor digitorum brevis

Function: Flexes the four lateral toes at their proximal interphalangeal joints (P2-P3); Innervation: Medial plantar nerve (branch of tibial nerve, S1-S3); Delicate, slightly fleshy muscle arising distal to the carpus.

mm. lumbricales

Function: Flexion of the metacarpophalangeal joints (P1-P2); Innervation: Deep branch of n. ulnaris; Associated with the tendons of m. flexor digitorum profundus.

mm. interossei

Function: Aid in flexion of digits and stabilization of joints; Innervation: Deep branch of n. ulnaris; Lie deep to the tendons of digital flexors on palmar side of metacarpals.

m. abductor digiti I longus

Function: Abduction of the first digit; Innervation: Radial nerve; Long, spindle-shaped muscle arising from lateral side of radius/ulna.

m. flexor digiti I brevis

Function: Flexes digit I; Innervation: Median or ulnar nerve; Located on palmar side of digit I.

m. abductor digiti II

Function: Abduction of second digit; Innervation: Ulnar nerve; Small palmar muscle on digit II.

m. abductor digiti V

Function: Abducts fifth digit; Innervation: Ulnar nerve; Lies on medial side of paw, near digit V.

m. extensor digitorum brevis

Function: Extends the digits; Innervation: N. fibularis; Flat muscle, 2.5-3 cm wide; lies on the distal row of tarsal bones and metatarsals.

lumbricales

Function: Flexion at the metatarsophalangeal joints, assist in digit stabilization. Innervation: (Not explicitly stated, but typically by branches of tibial nerve). Lie between deep flexor tendon branches; covered by mm. interflexorii and suspensory ligament.

mm. interflexorii

Function: Help stabilize tendons and assist in plantar flexion of the digits. Innervation: (Not specified; typically tibial nerve). Two flat, relatively large muscles shorter than the thoracic limb counterpart.

mm. adductores digiti II et V

Function: Adduction of digits II and V. Innervation: (Not specified; typically tibial nerve). Lie on the plantar surface of mm. interossei.

m. quadratus plantae

Function: Assists flexor digitorum profundus by redirecting pull. Innervation: (Not stated; usually tibial nerve). Tarsal head of m. flexor digitorum profundus; arises from calcaneus and lateral collateral tarsal ligament.

m. sacrocaudalis dorsalis lateralis

Function: Extension or lifting of the tail; possibly moves tail laterally. Innervation: Branches of the caudal dorsal plexus. Flat, segmental muscle that enlarges dorsally.

m. sacrocaudalis dorsalis medialis

Function: Extends and may laterally flex the tail. Innervation: Branches of the caudal dorsal plexus. Direct continuation of m. multifidus; made of short segments.

m. intertransversarius dorsales caudae

Function: Stabilizes and assists in tail extension and lateral movement. Innervation: Branches of caudal nerves. Small segmental dorsal muscles between vertebrae.

m. sacrocaudalis ventralis lateralis

Function: Flexes tail downward and laterally. Innervation: Branches of the caudal ventral plexus. Prominent in large dogs; ends in long tendons.

m. sacrocaudalis ventralis medialis

Function: Same as lateral counterpart: flexion and lateral movement. Innervation: Branches of the caudal ventral plexus. Segmental structure along entire tail.

m. intertransversarius ventrales caudae

Function: Assists ventral tail movement. Innervation: Caudal spinal nerves. Small muscles between ventral processes of caudal vertebrae.

m. coccygeus

Function: Presses tail downward and to one side. Innervation: Sacral nerves. Lies lateral to m. levator ani.

m. levator ani

Function: Elevates anus and supports rectum. Innervation: Sacral spinal nerves. Fan-shaped; blends with internal anal sphincter.

m. rectococcygeus

Function: Pulls rectum and anus cranially after defecation. Innervation: Pelvic nerves. Smooth muscle extension from rectum to tail base.

m. sphincter ani internus

Function: Involuntary control of anal tone. Innervation: Autonomic innervation (pelvic plexus).

m. sphincter ani externus

Function: Voluntary control of anal closure. Innervation: Pudendal nerve. Encircles the anus externally.

m. retractor penis / clitoridis

Function: Retracts penis or clitoris. Innervation: Pudendal nerve. Associated with the tail base and perineum.