|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|only to the level of the base of the fifth metatarsal. On the medial side of the ankle (Fig. 442) the sheath for the Tibialis posterior extends highest upto about 4 cm. above the tip of the malleoluswhile below it stops just short of the tuberosity of the navicular. The sheath for Flexor hallucis longus reaches up to the level of the tip of the malleolus, while that for the Flexor digitorum longus is slightly higher; the former is continued to the base of the first metatarsal, but the latter stops opposite the first cuneiform bone.|
| On the lateral side of the ankle (Fig. 441) a sheath which is single for the greater part of its extent encloses the Peronæi longus and brevis. It extends upward for about 4 cm. above the tip of the malleolus and downward and forward for about the same distance.|
|8e. The Muscles and Fasciæ of the Foot|
1. The Dorsal Muscle of the Foot
Extensor digitorum brevisThe fascia on the dorsum of the foot is a thin membranous layer, continuous above with the transverse and cruciate crural ligaments; on either side it blends with the plantar aponeurosis; anteriorly it forms a sheath for the tendons on the dorsum of the foot.
| The Extensor digitorum brevis (Fig. 441) is a broad, thin muscle, which arises from the forepart of the upper and lateral surfaces of the calcaneus, in front of the groove for the Peronæus brevis; from the lateral talocalcanean ligament; and from the common limb of the cruciate crural ligament. It passes obliquely across the dorsum of the foot, and ends in four tendons. The most medial, which is the largest, is inserted into the dorsal surface of the base of the first phalanx of the great toe, crossing the dorsalis pedis artery; it is frequently described as a separate musclethe Extensor hallucis brevis. The other three are inserted into the lateral sides of the tendons of the Extensor digitorum longus of the second, third, and fourth toes.|
Variations.Accessory slips of origin from the talus and navicular, or from the external cunei-form and third metatarsal bones to the second slip of the muscle, and one from the cuboid to the third slip have been observed. The tendons vary in number and position; they may be reduced to two, or one of them may be doubled, or an additional slip may pass to the little toe. A supernumerary slip ending on one of the metatarsophalangeal articulations, or joining a dorsal interosseous muscle is not uncommon. Deep slips between this muscle and the Dorsal interossei occur.
Nerves.It is supplied by the deep peroneal nerve.
Actions.The Extensor digitorum brevis extends the phalanges of the four toes into which it is inserted, but in the great toe acts only on the first phalanx. The obliquity of its direction counteracts the oblique movement given to the toes by the long Extensor, so that when both muscles act, the toes are evenly extended.
2. The Plantar Muscles of the Foot
Plantar Aponeurosis (aponeurosis plantaris; plantar fascia).The plantar aponeurosis is of great strength, and consists of pearly white glistening fibers, disposed, for the most part, longitudinally: it is divided into central, lateral, and medial portions.
| The central portion, the thickest, is narrow behind and attached to the medial process of the tuberosity of the calcaneus, posterior to the origin of the Flexor digitorum brevis; and becoming broader and thinner in front, divides near the heads of the metatarsal bones into five processes, one for each of the toes. Each of these processes divides opposite the metatarsophalangeal articulation into two strata, superficial and deep. The superficial stratum is inserted into the skin of