384 PRACTICAL ANATOMY. 



Externally, by the flexor longns hallucis ; internally, by the flexor longus digi- 

 torum ; its floor is the tibialis posticus, flexor longus digitorum, tibia, and internal 

 lateral ligament ; its roof, the deep transverse fascia, described in a previous 

 paragraph. 



Deep Muscles of the Leg. (i) Popliteus ; (2) flexor longus hallucis ; (3) 

 flexor longus digitorum ; (4) tibialis posticus. It is necessary now to study 

 the posterior surfaces of the tibia. (Fig. 208.) Notice that the oblique line of 

 the tibia has three lips : (i) An upper one, occupied by the insertion of the pop- 

 liteus muscle ; (2) a middle one, by the soleus ; (3) a lower one, by two muscles 

 the flexor longus digitorum on the outer side of the vertical line, and the tibialis 

 posticus on the inner side. Notice, too, that the posterior surface of the fibula 

 (Fig. 208) is occupied by the origin of two muscles : the outer head of the soleus, 

 the upper one-third, and the flexor longus hallucis, the middle one-third, of this 

 posterior surface. 



What can be said regarding t/ic rather peculiar origin and insertion of the flexor 

 longus digitorum and flexor longus Jiallucis f 



They arise from surfaces of bone above, opposite their insertions, into the 

 phalanges below : The great toe is on the side opposite the fibula ; the four 

 lesser toes are on the side opposite the tibia. Now, the muscle that bends the 

 great toe flexor longus hallucis arises from the posterior surface of the fibula, 

 middle one-third ; likewise, the muscle that bends the four lesser toes the flexor 

 longus digitorum arises from the posterior surface of the tibia, middle one-third. 

 To gain their insertions they cross in the sole of the foot in the second layer ot 

 muscles of this region. (Fig. 270.) 



The flexor longus hallucis traverses four grooves. (Fig. 268.) The flexor 

 longus hallucis needs special mention. It passes through (i) a little groove on 

 the posterior part of the tibia (Fig. 208) ; (2) through a pronounced one on the 

 narrow posterior surface of the astragalus ; (3) through a well-marked groove 

 on the under part of the sustentaculum tali of the os calcis (Fig. 268) ; 

 (4) through a groove between the two sesamoid bones,, in the tendon of the 

 flexor brevis hallucis at the metatarso-phalangeal articulation. This muscle is 

 inserted into the base of the distal phalanx of the great toe. (Fig. 268.) 



Trace the popliteus muscle to its origin. (Fig. 266.) Detach it at the ob- 

 lique line of the tibia, its insertion, and trace it between the outer tuberosity and 

 head of fibula, under the external lateral ligament of the knee and the biceps, to 

 the outer side of the external condyle of the femur. 



Structures under Internal Annular Ligament. From the internal malleo- 

 lus to the os calcis : (i) Tendon of tibialis posticus, next the malleolus ; (2) ten- 

 don of flexor longus digitorum ; (3) a sheath of connective tissue containing the 

 posterior tibial nerve and artery, with a vein on each side of the artery ; (4) behind 

 this sheath, and deeply buried in its three upper grooves, above referred t<>, is 

 the tendon of the flexor longus pollicis. In the dissection of the sole of the foot 

 these several structures will be traced to their various destinations. 



The Peronei Longus and Brevis ( Figs. 266 and 269). These two muscles 

 occupy almost the entire outer surface of the fibula. Commonly, the origin is as 

 follows : the longus from the upper one-third and the brevis from the middle 

 one-third. (Fig. 207.) The muscles are separated in front and behind from 

 adjacent musculatures by intermuscular septa. They pass under the external 

 annular ligament, immediately behind the malleolus, and are inserted : ( f) the 

 brevis into the base of the fifth metatarsal ( Fig. 269) ; (2) the longus pa>ses 

 through a groove on the under surface of the cuboid bone, then through an 

 osseo-aponeurotic canal, to the base of the first metatarsal bone. (Fig. 275.) 

 These muscles are supplied by muscular branches of the nnusculo-cutaneous 

 IH.TVC, a branch of the external popliteal. (Fig. 264.) These muscles, when 



