252 MUSCLES OF THE LOWER LIMB. 



The plantaris muscle arises from the femur immediately above the 

 external condyle, and from the posterior ligament of the knee-joint ; 

 its muscular part is from three to four inches in length, and terminates 

 in a long delicate tendon, which inclines inwards between the gastro- 

 cnemius and soleus, and, running along the inner border of the tendo 

 Achillis,is inserted not far from it into the posterior part of the calcaneum. 



Varieflcft. — The plantaris varies in its mode of termination ; it is sometimes 

 enclosed in the lower i^art of the tendo Achillis ; and, in other cases, it ends in 

 the internal annular ligament, which binds down the tendons and vessels behind 

 the inner malleolus. It is not unfrequently absent altogether. This muscle, which 

 is little develoiied and almost vestigial in man, is sometimes of large size in 

 animals, and in some is continued forward in the sole of the foot as a part of the 

 flexor muscles of the toes. 



The DEEP GROUP of posterior muscles of the leg is in close contact 

 with the bones ; it consists of the popliteus, flexor longus digitorum, 

 flexor longus pollicis, and tibialis posticus. 



The popliteus, an oblique muscle placed below the knee, arises by a 

 thick tendon, about an inch in length, from the fore part of the 

 po})liteal groove on the outer surface of the external condyle of the 

 femur, within the external lateral ligament and capsule of the knee-joint ; 

 it is in contact with the external semilunar cartilage, and receives 

 additional fibres from the posterior ligament of the joint. The mus- 

 cular fibres diverge as they pass downwards, and are inserted into 

 the triangular surface of the tibia above the posterior oblique line. 



The tendon of the popliteus muscle occupies the groove on the outside 

 of the femur in flexion only. 



liclat'iuitx. — The popliteus is bound do\vn by an aponeurosis, principally derived 

 from the tendon of the semimembranosus muscle. The plantaris and gastro- 

 cnemius muscle, the popliteal vessels and internal popliteal neiTe lie upon its 

 IDOsterior surface. 



The three remaining muscles of this group are bound down together 

 by a deep fascia, which extends between the tibia and fibula, and sepa- 

 rates them from the soleus. 



The flexor longus digitorum pedis muscle, or flexor perforans, 



arises from the posterior surface of the tibia, in a space extending from 

 the oblique line to within three inches of the inner ankle ; it likewise 

 arises in comiection with the flexor longus pollicis, by aponeurotic fibres, 

 which pass over the surface of the tibialis posticus. Its tendon descends 

 in a groove behind the internal malleolus, lying on that of the tibialis 

 posticus, and invested by a distinct fibrous and synovial sheath ; it is 

 then directed under the arch of the os calcis, obliquely forwards and 

 outwards, into the sole of the foot, crossing the tendon of the flexor 

 longus pollicis inferiorly, and connected with it by a tendinous slip ; it 

 then divides into four parts, which pass forwards to be inserted into 

 the terminal phalanges of the four smaller toes. Each digital tendon 

 enters a fibrous sheath on the toe to which it belongs, perforates the 

 corresponding tendon of the flexor brevis digitorum, and is invested 

 with synovial membrane, and connected by viucula accessoria to the 

 [ihalanges ; the whole arrangement being essentially the same as that 

 which has been already described in the fingers. 



Rdatlona. — It rests upon the ti1)ia and upon the inner surface of the tibialis 

 posticus, the tendon of which it also crosses about two inclies above the ankle. 



