400 THE INFERIOR EXTREMITY 



between the heads of the various metatarsal bones. The toes 

 can then be separated more freely from each other, and the 

 interosseous muscles traced to their insertions. It is well, at 

 this stage, to reflect the flexor digiti quinti brevis also. 



Interosseous Muscles. There are seven interosseous 

 muscles, three plantar and four dorsal. The plantar inter- 

 osseous muscles are so placed that they adduct the lateral three 

 toes towards the middle line of the second toe. They arise 

 from the plantar aspects and parts of the medial surfaces of 

 the lateral three metatarsal bones, and each is inserted upon 

 the medial side of the first phalanx of the corresponding toe. 

 The dorsal interosseous muscles occupy the four intermetatarsal 

 spaces, and consequently they must be dissected upon both 

 plantar and dorsal aspects of the foot. They are arranged so 

 as to abduct the second, third, and fourth toes from the 

 middle line of the second toe. Each arises by two heads 

 from the dorsal parts of the adjacent sides of the metatarsal 

 bones which bound the cleft in which it lies. They are 

 inserted as follows : \hz first, upon the medial side of the first 

 phalanx of the second toe ; the second, upon the lateral side 

 of the same phalanx ; the third, upon the lateral side of the 

 first phalanx of the third toe ; and the fourth, upon the lateral 

 side of the first phalanx of the fourth toe. The slender 

 tendons of the interosseous muscles are only very slightly 

 attached to the bases of the proximal phalanges. They are 

 inserted for the most part into the expansions of the extensor 

 tendons on the dorsal aspect of the toes (p. 346). 



Tendons of the Tibialis Posterior and Peronseus Longus. 

 Before leaving the sole of the foot the dissector must deter- 

 mine the precise insertions of the tendons of the tibialis 

 posterior and of the peronaeus longus. The tendon of the 

 tibialis posterior is inserted not merely into the tuberosity 

 of the navicular bone. Fibrous slips are seen to spread out 

 from it, and these may be traced to every bone of the tarsus, 

 with the exception of the talus, and also to the bases of the 

 second, third, and fourth metatarsal bones. As it lies under 

 and gives support to the head of the talus, the tendon of the 

 tibialis posterior has developed within it a sesamoid nodule 

 of fibro-cartilage, and in some cases a sesamoid bone 

 (Fig. 103). 



The tendon of the peronczus longus turns round the 

 lateral margin of the foot, and runs medially, across the 



