I. Osteology

• A. tarsus: 7 tarsals
• B. metatarsals: 5; enumerated from medial to lateral
• C. phalanges: total of 14; two on the hallux and three on each of the lateral 4 digits

II. Arthrology

• A. longitudinal arch - the foot is arched from front to back to resist deformation; subdivided into medial and lateral portions
• B. transverse arch - epiphenomenon (non-functional byproduct) of the different curvatures of the medial and lateral divisions of the longitudinal arch
• C. ligaments maintaining longitudinal arch
  • 1. plantar calcaneonavicular (spring) extends from sustenaculum tali to navicular; supports medial portion of longitudinal arch; stretching results in collapse of medial longitudinal arch (flat foot)
  • 2. long plantar - extends from calcaneus and cuboid to base of metatarsals; supports lateral portion of longitudinal arch
  • 3. short plantar - extends from calcaneus to cuboid; supports lateral longitudinal arch
• D. plantar aponeurosis - thick, fibrous aponeurosis deep to superficial fascia of sole of foot; functions in support of longitudinal arch

III. Myology (intrinsic muscles of the foot; act upon the metatarsophalangeal and interphalangeal joints)

• A. Dorsal - innervated by the deep fibular (peroneal) nerve
  • 1. extensor digitorum brevis - extends digits 2-4
  • 2. extensor hallucis brevis - extends the hallux
• B. Plantar - lie in 3 muscle compartments; innervated by the medial and lateral plantar nerves
  • 1. medial compartment - innervated by medial plantar nerve
    • a. abductor hallucis - abducts hallux
    • b. flexor hallucis brevis - flexes hallux
  • 2. lateral compartment - innervated by lateral plantar nerve
    • a. abductor digiti minimi (quinti) - abducts digit 5
    • b. flexor digiti minimi brevis - (what happened to longus?) flexes digit 5
  • 3. middle compartment - arranged in 4 layers
    • a. layer 1 - flexor digitorum brevis - medial plantar n.; flexes digits 2-5
    • b. layer 2 - 2 muscle groups associated with tendons of FDL
      • i. quadratus plantae - lateral plantar n.; aids FDL
      • ii. lumbricals - 4; first by medial plantar n.; lateral 3 by lateral plantar n.; possibly act like manual lumbricals
    • c. layer 3 - adductor hallucis: lateral plantar n.; adduct hallux
    • d. layer 4 - interossei; in the foot the axis of abduction/adduction passes through D2 rather than D3 in the hand; innervated by lateral plantar n.
      • i. plantar interossei - 3, adduct digits 3-5
      • ii. dorsal interossei - 4; abducts digits 2-4
  • 4. function - the intrinsic foot musculature's actions about the metatarsophalangeal and interphalangeal joints are of minimal significance; muscles spanning the longitudinal arch (abductor hallucis, abductor digiti minimi and flexor digitorum brevis) can support the arch under conditions of increased load

IV. Vessels

• A. Dorsal - dorsalis pedis artery is a direct continuation of the anterior tibial artery at the ankle.
• B. Plantar - posterior tibial artery terminates deep to the flexor retinaculum by dividing into the medial and lateral plantar arteries

V. Correspondence of Volar and Plantar Musculature

Volar					Plantar
thenar compartment					medial compartment
	abductor pollicis brevis		median n.			medial plantar n.		abductor hallucis
	flexor pollicis brevis		median n.			medial plantar n.		flexor hallucis brevis
	oppens pollicis		median n.			-		-
hypothenar compartment					lateral compartment
	abductor digiti minimi		ulnar n.			lateral plantar n.		abductor digiti minimi
	flexor digiti minimi brevis		ulnar n.			lateral plantar n.		flexor digiti minimi
	oppens digiti minimi		ulnar n.			-		-
central compartment					middle compartment
	[extrinsic: FDPsupf]		median n.			medial plantar n.		flexor digitorum brevis
	-		-			lateral plantar n.		quadratus plantae
	lumbricals 1-2		median n.			medial plantar n.		lumbrical 1
	lumbricals 3-4		ulnar n.			lateral plantar n.		lumbricals 2-4
	adductor pollicis		ulnar n.			lateral plantar n.		adductor hallucis
	palmer interossei		ulnar n.			lateral plantar n.		plantar interossei
	dorsal interossei		ulnar n.			lateral plantar n.		dorsal interossei

V. Hindlimb Sensory Innervation

• This link contains figures and text describing the cutaneous and segmental innervation of the hindlimb. This material will not be covered on the exam but is supplied for future reference since if forms the basis, in part, for distinguishing peripheral and central nervous system deficiencies.