MUSCLES OF THE SOLE OF THE FOOT. 273 



The MUSCULUS ACCESSORIUS arises by two slips from either side 

 of the under surface of the os calcis ; the inner slip being fleshy, the 

 outer tendinous. The muscle is inserted into the outer side and upper 

 surface of the tendon of the flexor longus digitorum. 



Relations. By its superficial surface with the three muscles of the 

 superficial layer, from which it is separated by their fascial sheaths, 

 and with the external plantar vessels and nerves. By its deep surface 

 with the under surface of the os calcis and the long calcaneo-cuboid 

 ligament. 



The LUMBRICALES (lumbricus, an earthworm) are four little muscles 

 arising from the tibial side of the tendons of the flexor longus digi- 

 torum, and inserted into the expansion of the extensor tendons, and 

 into the base of the first phalanx of the four lesser toes. 



Relations. By their superficial surface with the tendons of the 

 flexor brevis digitorum. By their deep surface with the third layer 

 of muscles of the sole of the foot. They pass between the digital slips 

 of the deep fascia to reach their insertion. 



Third Layer. 



Flexor brevis pollicis, 

 Abductor pollicis, 

 Flexor brevis minimi digiti, 

 Transversus pedis. 



Dissection. The tendons of the long flexors and the muscles con- 

 nected with them must be removed, to see clearly the attachments of 

 the third layer. 



The FLEXOR BREVIS POLLICIS arises by a pointed tendinous pro- 

 cess from the side of the cuboid, and from the external cuneiform bone ; 

 it is inserted by two heads into the base of the first phalanx of the 

 great toe. Two sesamoid bones are developed in the tendons of inser- 

 tion of these two heads, and the tendon of the flexor longus pollicis 

 lies in the groove between them. 



Relations. By its superficial surface with the abductor pollicis, ten- 

 don of the flexor longus pollicis, and plantar fascia. By its deep 

 surface with the tarsal bones and their ligaments, the metatarsal bone 

 of the great toe, and the insertion of the tendon of the peroneus 

 longus. By its inner border with the abductor pollicis ; and by its 

 outer border with the adductor pollicis ; with both of these muscles it 

 is blended near its insertion. 



The ADDUCTOR POLLICIS arises from the cuboid bone, from the 

 sheath of the tendon of the peroneus longus, and from the base of the 

 third and fourth metatarsal bones. It is inserted into the base of the 

 first phalanx of the great toe. 



Relations. By its superficial surface with the tendons of the flexor 

 longus and flexor brevis digitorum, the musculus accessorius, and lum- 

 bricales. By its deep surface with the tarsal bones and ligaments. 



