=M. quadratus plantæ= (called also the plantar head of the flexor longus digitorum) is a thin flat muscle which takes _origin_ from the dorsal part of the lateral surface of the calcaneus and the cuboid. Its fibres converge to a flat tendon which passes transversely across the flexor longus digitorum and beneath the flexor brevis digitorum and calcaneometatarsal. _Insertion._--Into the medial part of the outer surface of the tendon of the flexor longus digitorum. _Action._--It holds the flexor longus tendon in place. =Mm. lumbricales.=--These are six. _Origin._--The three larger ones have origin from the outer surface of the expanded portion of the flexor longus digitorum on its distal half. Each ends in a slender tendon. _Insertions._--The tendons unite with the divisions of the tendon of the flexor brevis which pass to the three lateral digits, at their entrance to the first annular ligament. The one to the fifth digit is sometimes absent. The other three have _origin_ from the tendon of the flexor longus digitorum at the point where it divides. Each occupies one of the three intervals between the four divisions, and its fibres originate from the proximal ends of the two tendons which bound its interval. _Insertion_ by a very slender tendon into the medial side of the first phalanges of the third, fourth, and fifth digits near their bases. _Action._--Move the third, fourth, and fifth digits toward the medial side. =Mm. interossei.=--The interosseus of the second digit forms five portions, which cover the ventral surface of the digit. _Origin._--(1) By two tendons from the ventral process of the lateral cuneiform. The muscle divides into four parts, three of which pass to the medial side of the digit and act as abductors. They are called the long, short, and middle abductors (abductor longus, brevis, and intermedius digiti secundi). _Insertions._--The short head into the medial sesamoid of the metatarsophalangeal joint, the middle into the medial side of the base of the first phalanx, and the long into the extensor communis tendon near the distal end of the first phalanx. The names long, short, and middle refer to the lengths of the tendons as determined by their points of insertion. The _fourth_ portion which comes from the lateral cuneiform has its _insertion_ into the lateral side of the extensor tendon near the distal end of the first phalanx. It is therefore an adductor longus digiti secundi. In some cases there is an adductor brevis from this same head. (2) The fifth part of the interosseus of the second digit has _origin_ from the middle of the ligament covering the peroneal canal, along with the middle adductor of the fifth digit. The two muscles diverge. _Insertion_ into the outer side of the base of the first phalanx of the second digit. It is an adductor medius digiti secundi. The interossei of the third and fourth digits are alike.