140 



MUSCLES OF THE LEG. 



muscles (lumbricales), which may also be con- 

 sidered as accessories to the flexor longus. 



When passing behind the inner malleolus, 

 this tendon is in contact with that of the tibialis 

 posticus, which lies close to the bone. They are 

 inclosed in separate sheaths of synovial mem- 

 brane. In the leg this muscle is bound down 

 by the deep fascia, and covered partly by the 

 posterior tibial vessels which separate it from 

 the soleus; its anterior surface rests against 

 the tibia, and overlaps the tibialis posticus 

 muscle ; in the foot, its tendon lies between 

 those of the flexor longus polhcis which are 

 above it, and the flexor brevis digitorum which 

 lies beneath it. 



3. Flexor longus pollicis is shorter but 

 stronger than the former muscle. It is si- 

 tuated the outermost of the three deep muscles 

 of the leg, in contact with the fibula. It arises 

 tendinous and fleshy from the lower half of 

 the posterior surface and outer edge of the 

 fibula, with the exception of the undermost 

 portion. The fleshy fibres terminate in a 

 tendon which passes behind the inner ankle, 

 through a groove in the tibia ; next through a 

 groove in the astragalus ; crosses in the sole of 

 the foot the tendon of the flexor longus digi- 

 torum, to which it gives a slip of tendon ; 

 passes between the t%vo heads of the flexor 

 brevis pollicis, and then runs in a sheath of 

 tendinous structure which binds it to the under 

 surface of the phalanx, and is inserted into the 

 base of the last phalanx of the great toe. The 

 relations of this muscle in the leg are, pos- 

 teriorly it is covered by the deep fascia, 

 which separates it from the soleus; anteriorly it 

 is in contact with the fibula, and overlaps the 

 tibialis posticus muscle and the peroneal ar- 

 tery. Its connections in the foot have been 

 explained above. The action of the flexor 

 longus pollicis is not confined to the great toe ; 

 by means of the slip of tendon, which it gives 

 to the flexor longus digitorum, it acts also 

 upon all the toes, and secondarily upon the 

 foot itself, assisting powerfully in the elevation 

 of the heel in progression. But the mode of 

 action of this muscle, and its complicated rela- 

 tions with the other muscles of the foot, are 

 too curious to be passed over with a slight ex- 

 amination ; in fact, we think it may clearly be 

 shewn that there is here one of the most curious 

 and beautiful arrangements and successions 

 of muscular action to be met with in the whole 

 system. ^\ e have elsewhere shewn that, from 

 the peculiar form of the foot, the action of the 

 peroneus longus is essential to transmit the 

 burden of progression from the weaker to the 

 stronger side of the foot. (See article FOOT, 

 MUSCLES OF.) Let us now follow on the pro- 

 gress of the foot in the act of walking, and we 

 shall readily perceive the succession of action 

 of its different parts, and the functions which 

 each muscle performs. It is evident that the 

 smaller toes being shorter than the large one, 

 and nearer to the heel, they will, in the act of 

 elevating the heel and propelling forward the 

 body, come to their bearing on the ground 

 somewhat before the great toe, their action 

 being, in fact, by the breadth of base which 



they give to steady the onward progress of the 

 body, and to deliver over accurately and se- 

 curely the weight to the great toe, the main 

 organ of propulsion of the body. In order to 

 accomplish this to the best effect, it is neces- 

 sary that the succession of actions should be 

 accurate and complete, and that the muscles of 

 the smaller toes should exert themselves be- 

 fore that of the great toe. To this end the 

 flexor longus pollicis gives a slip to the flexor 

 of the toes, and by the commencement of its 

 action, which merely firmly plants the great 

 toe against the ground, rouses the muscles of 

 the other toes, assisting them to complete 

 their part of the process, while its own labour 

 continues and is at its height when theirs is 

 necessarily accomplished and at an end. Thus, 

 by a beautiful combination and series of actions, 

 the powerful effort of the great extensors of the 

 foot is controlled and guided to its proper end, 

 first by the peronei, next by the flexors of the 

 smaller toes, assisted by the long flexor of the 

 great toe ; and the body propelled onwards 

 and balanced on this toe, the action is com- 

 pleted by the further effort of this one power- 

 ful muscle. The economy of muscular power 

 is here not less striking than the combination 

 of action, for the flexor longus pollicis being 

 inserted into the last phalanx of the great toe, 

 its own proper action is not called for till after 

 the muscles of the other toes have performed 

 their part; this muscle, therefore, considerably 

 the most powerful of all this deep layer, were 

 it not for the simple expedient of the slip of 

 communication to the other flexors, would be 

 comparatively useless until the last moment of 

 the propulsion onwards of the body. But now 

 it lends its powerful assistance to the weaker 

 muscles previous to its own peculiar effort, and 

 when all its power is called for, the collateral 

 demand has ceased. 



4. Tibialis posticus is situated on the back 

 of the leg between the last-named muscles. 

 It arises fleshy from the posterior surface both 

 of the tibia and fibula, immediately below the 

 upper articulations of these bones with each 

 other. Between the two portions of this at- 

 tachment is an angular opening through which 

 the anterior tibial vessels are transmitted. The 

 muscle also arises from the whole interosseous 

 ligament ; from the angles of the bones to 

 which that ligament is attached, and from two- 

 thirds of the flat posterior surface of the fi- 

 bula. The fibres run obliquely towards a 

 round tendon, which passes behind the inner 

 ankle, through a groove in the tibia. It is here 

 situated close to the bone enclosed in a sepa- 

 rate synovial sheath. It is inserted into the 

 tubercle on the plantar surface of the os navi- 

 culare, sending tendinous filaments to most of 

 the other bones of the tarsus, and to the meta- 

 tarsal bones of the second and middle toes. 

 This muscle is covered at the lower part of its 

 origin by the flexor longus digitorum and flexor 

 longus pollicis, and cannot be seen till those 

 muscles are separated. But superiorly it is 

 covered by the soleus only, and here the poste- 

 rior tibial vessels rest upon it. Its anterior 

 surface is in contact with the interosseous ligu- 



