Final answer:
The intrinsic muscles of the foot include the dorsal group with extensor digitorum brevis and the plantar group with four layers: dorsal interossei, plantar interossei, lumbricals, and flexor digitorum brevis. These muscles aid in toe movements and support the foot's arch.
Step-by-step explanation:
Intrinsic Muscles of the Foot
The intrinsic muscles of the foot - 4 layers are crucial for the movements and support of the foot. These muscles can be categorized into two groups: the dorsal group and the plantar group. The dorsal group consists of the extensor digitorum brevis, and it generally helps extend the toes. In contrast, the plantar group comprises four layers. Starting with the most superficial, these layers provide strength essential for counterbalancing the body's weight and supporting the foot's arch.
Dorsal interossei (layer a) - Help extend the toes and abduct the second to fourth toes.
Plantar interossei (layer b) - Located underneath the plantar skin, generally help to flex and adduct the third to fifth toes.
Lumbricals (layer c) - Arising from the tendons of the flexor digitorum longus, these muscles help in flexing the metatarsophalangeal joints and extending the interphalangeal joints.
Flexor digitorum brevis (layer d) - The top-most layer, located just inferior to the foot and toe bones, assists in flexing the toes.
These intrinsic muscles, similar to those in the hand, also contribute to the stability of the foot's arch, especially the longitudinal arch supported by the plantar aponeurosis.