THE PLANTAR MUl 



)F THE FOOT 



491 



the transverse sulcus which separates the toes from the sole. The deeper stratum 

 divides into two slips which embrace the side of the Flexor tendons of the toes, 

 and blend with the sheaths of the tendons, and 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 to become 

 superficial. At the point of division of the aponeurosis, numerous transverse 

 fasciculi are superadded ; these serve to increase the strength of the aponeurosis 

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

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

 and medial portions and sends upward into the foot, at the lines of junction, two 

 strong vertical intermuscular septa, broader in front than behind, which separate 

 the intermediate from the lateral and medial plantar groups of muscles; from these 

 again are derived thinner transverse septa which separate the various layers of 

 muscles in this region. The upper surface of this aponeurosis gives origin behind 

 to the Flexor digitorum brevis. 



The lateral and medial portions of the plantar aponeurosis are thinner than 

 the central piece, and cover the sides of the sole of the foot. 



The lateral portion covers the under surface of the Abductor digiti quinti; it is 

 thin in front and thick behind, where it forms a strong band between the lateral 

 process of the tuberosity of the calcaneus and the base of the fifth metatarsal bone; 

 it is continuous medially with the central portion of the plantar aponeurosis, and 

 laterally with the dorsal fascia. 



The medial portion is thin, and covers the under surface of the Abductor hallucis; 

 it is attached behind to the laciniate ligament, and is continuous around the side 

 of the foot with the dorsal fascia, and laterally with the central portion of the plantar 

 aponeurosis. 



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

 in a similar manner to those in the hand. Those of the medial plantar region 

 are connected w y ith the great toe, and corrrespond with those of the thumb ; those 

 of the lateral plantar region are connected with the little toe, and correspond with 

 those of the little finger; and those of the intermediate plantar region are connected 

 with the tendons intervening between the two former groups. But in order to 

 facilitate the description of these muscles, it is more convenient to divide them into 

 four layers, in the order in which they are successively exposed. 



Abductor hallucis. 



The First Layer (Fig. 443). 



Flexor digitorum brevis. 

 Abductor digiti quinti. 



The Abductor hallucis lies along the medial border of the foot and covers the 

 origins of the plantar vessels and nerves. It arises from the medial process of the 

 tuberosity of the calcaneus, from the laciniate ligament, from the plantar aponeu- 

 rosis, and from the intermuscular septum between it and the Flexor digitorum 

 brevis. The fibers end in a tendon, which is inserted, together with the medial 

 tendon of the Flexor hallucis brevis, into the tibial side of the base of the first 

 phalanx of the great toe. 



Variations. Slip to the base of the first phalanx of the second toe. 



The Flexor digitorum brevis lies in the middle of the sole of the foot, imme- 

 diately above the central part of the plantar aponeurosis, with which it is firmly 

 united. Its deep surface is separated from the lateral plantar vessels and nerves 



