292 INFERIOR EXTREMITY 



formed by the base of the fifth metatarsal bone and the 

 lateral tuberosity of the calcaneus. 



In connection with the plantar aponeurosis two inter- 

 muscular septa have also to be studied. These pass dorsally 

 into the sole, along the lines of the longitudinal furrows 

 which mark off the intermediate from the medial and lateral 

 parts of the aponeurosis. They consequently lie one upon 

 either side of the flexor digitorum brevis, and form partitions 

 which separate it from the abductor hallucis on the one side, 

 and the abductor digiti quinti on the other. 



Dissection. To demonstrate these septa, make a transverse incision 

 through the intermediate portion of the plantar aponeurosis, about an inch 

 in front of the medial tuberosity of the calcaneus, and also a longitudinal 

 cut through the same piece of aponeurosis, extending from the first incision 

 along the middle line of the foot. Now raise the divided fascia and throw 

 it laterally and medially. Some difficulty will be experienced in effecting 

 this, owing to its affording a surface of origin, in its posterior part, to the 

 subjacent flexor digitorum brevis. As the margins of this muscle are 

 approached the septa are brought into view. 



Muscles and Tendons of the Sole. It is customary to 

 look upon the muscles and tendons which we find in the 

 dissection of the sole as being disposed in four strata, viz. : 



f Abductor hallucis. 

 First layer. -! Flexor digitorum brevis. 



^ Abductor digiti quinti. 



( Tendon of flexor digitorum longus. 



I M. quadratus plantoe. 

 Second layer. | Lumbrical muscles. 



V. Tendon of flexor hallucis longus. 



I Flexor hallucis brevis. 

 Third layer. -! Adductor hallucis, oblique and transverse heads. 



\ Flexor brevis digiti quinti. 



I Interosseous muscles. 

 Fourth layer. -| Tendon of the peronaeus longus. 



l v Tendon of the tibialis posterior. 



Dissection. The lateral and medial portions of the plantar aponeurosis 

 should be raised from the subjacent muscles. The three superficial muscles 

 of the sole are then exposed to view and their connections can be studied. 

 The flexor digitorum brevis is placed intermediately, the abductor digiti 

 quinti extends along the lateral margin of the sole, and the abductor 

 hallucis along the medial margin of the sole. In the interval between 

 the abductor hallucis and flexor digitorum brevis the medial plantar nerve 

 and artery will be found. Follow the nerve toward the toes and dissect 

 out its four common digital branches. In doing so, care must be taken of 

 the muscular twigs which are given to the flexor hallucis brevis and the most 

 medial lumbrical muscle. Slender branches of the medial plantar artery 

 accompany the common digital nerves. Now traqe the trunk of the medial 

 plantar nerve posteriorly, by carefully separating the flexor digitorum brevis 



