THE PLANTAR REGION 539 



Nerves. It is supplied by the anterior tibial nerve. 



Actions. The Extensor brevis digitorum is an accessory to the long Extensor, extending the 

 phalanges of the four inner toes, but acting only c.i the first phalanx of the great toe. The 

 obliquity of its direction counteracts the oblique movement given to the toes by the long 

 Extensor, so that, both muscles acting together, the toes are evenly extended. 



9. The Plantar Region (Figs. 398, 399). 



The plantar fascia (aponeurosis plantar is], the densest of all the fibrous mem- 

 branes, is of great strength, and consists of pearly white glistening fibres, dis- 

 posed, for the most part, longitudinally; it is divided into a central and two 

 lateral portions. 



The central portion, the thickest, is narrow behind and attached to the inner 

 tubercle of the os calcis, posterior to the origin of the Flexor brevis digitorum, 

 and, becoming broader and thinner in front, divides near the heads of the meta- 

 tarsal 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 the transverse 

 sulcus which divides the toes from the sole. The deeper stratum divides into two 

 slips which embrace the sides of the Flexor tendons of the toes, and blend with the 

 sheaths of the tendons, and laterally with the transverse metatarsal ligament, thus 

 forming a series of arches through which the tendons of the short and long Flexors 

 pass to the toes. The intervals left between the five processes allow the digital 

 vessels and nerves and the tendons of the Lumbricales muscles to become super- 

 ficial. At the point of division of the fascia into processes and slips numerous 

 transverse fibres are superadded, which serve to increase the strength of the fascia 

 at this part by binding the processes together and connecting them with the integu- 

 ment. The central portion of the plantar fascia is continuous with the lateral 

 portions at each side, and from its deep surface sends upward two strong 

 vertical intermuscular septa, which separate the middle from the external and 

 internal groups of plantar muscles; from these, again, thinner transverse septa are 

 derived, which separate the various layers of muscles in this region. The deep 

 surface of this fascia gives attachment behind to the Flexor brevis digitorum muscle. 



The lateral portions of the plantar fascia are thinner than the central division, and 

 cover the sides of the foot. The outer portion covers the under surface of the 

 Abductor minimi digiti; it is thick behind, thin in front, and extends from the 

 os calcis to the base of the fifth metatarsal bone, to the outer side of which it is 

 attached; it is continuous internally with the central portion of the plantar fascia, 

 and externally with the dorsal fascia. The inner portion is very thin, and covers 

 the Abductor hallucjs muscle; it is attached to the internal annular ligament, and 

 is continuous around the side of the foot with the dorsal fascia, and externally with 

 the middle portion of the plantar fascia. 



The muscles in the plantar region of the foot may be divided into three groups, 

 in a similar manner to those in the hand: (1) Those of the internal plantar region 

 are connected with the great toe, and correspond with those of the thumb; (2) 

 those of the external plantar region are connected with the little toe, and corre- 

 spond with those of the little finger; and (3) those of the middle plantar region are 

 connected with the tendons intervening between the two former groups. But in 

 order to facilitate the dissection of these muscles it will be found more convenient 

 to divide them into four layers, as they present themselves, in the order in which 

 they are successively exposed. 



