556 A MANUAL OF ANATOMY 



Flexor Brevis Minimi Digiti — Origin. — (i) The plantar surface 

 of the base of the fifth metatarsal bone, and (2) the sheath of the 

 tendon of the peroneus longus. 



Insertion. — The outer side of the base of the first phalanx of the 

 little toe, in conjunction with the abductor minimi digiti. A few 

 of the fibres also take attachment to the plantar surface of the shaft 

 of the fifth metatarsal bone over its anterior part. These fibres 

 represent the muscle called opponens minimi digiti, the origin of 

 which corresponds with those fibres of the flexor brevis minimi 

 digiti which spring from the sheath of the tendon of the peroneus 

 longus. 



Nerve-supply. — The superficial division of the external plantar 

 nerve, and usually the outer digital branch of that division to the 

 outer side of the little toe. 



Action. — To flex the metatarso-phalangeal joint of the little toe. 

 The muscle is a small fleshy slip which lies upon the plantar surface 

 of the fifth metatarsal bone, under cover of the abductor minimi 

 digiti. It is liable to be taken for a plantar interosseous muscle, 

 lying, as it does, in close contact with the most external plantar 

 interosseous. 



Plantar Triangle. — This is a muscular triangle in connection with 

 the third layer of muscles, the boundaries of which are as follows : 

 Anterior or Base. — Adductor transversus hallucis. Internal.— 

 Adductor obliquus hallucis. External. — Flexor brevis minimi 

 digiti. Floor. — Portions of the plantar and dorsal interosseous 

 muscles, covered by the interosseous fascia. Roof .—The long flexor 

 tendons and the lumbricales. Contents. — (i) A limited portion of 

 the deep part of the external plantar artery ; (2) some of the digital 

 branches of the plantar arch, especially the second and third, and 

 the corresponding veins ; and (3) a limited portion of the deep 

 division of the external plantar nerve. 



Fourth Layer. — The fourth layer consists of the interosseous 

 muscles ; the tendon of the peroneus longus ; and the tendon of the 

 tibialis posticus. 



Interosseous Muscles. — The interosseous muscles are seven in 

 num.ber, and are arranged in two groups — plantar, of which there 

 are three, and dorsal, of which there are four. The plantar muscles 

 are seen only in the sole, but the dorsal muscles are seen on the 

 dorsum of the foot as well as in the sole. The plantar aspects of 

 the muscles are covered by the thin interosseous fascia which joins 

 anteriorly the transverse metatarsal ligament. 



Plantar Interossei. — These belong to the three outer toes, and 

 are named first, second,, and third from within outwards. 



Origin. — (i) The inner surfaces of the shafts of the third, fourth, 

 and fifth metatarsal bones, and (2) the sheath of the tendon of the 

 peroneus longus. 



Insertion. — (i) The inner sides of the bases of the first phalanges 

 of the third, fourth, and fifth toes, and (2) the expansions formed 

 by the long and short extensor tendons (in the case of the fifth toe 



