654 



HUMAN ANATOMY. 



{cc) The Deep Layer. 



I. Tibialis posticus. 2. Flexor accessorius. 



3. Popliteus. 



I. Tibialis Posticus (Fig. 621). 



Attachments. — The posterior tibial (m. tibialis posterior) arises from the pos- 

 terior surface of the interosseous membrane and from the adjacent surface of both 

 the tibia and fibula. Its fibres pass into a tendon, situated along its inner border, 

 which passes obliquely downward and inward beneath the ilexor longus digitorum. 

 It is continued onward beneath the most central portion of the internal annular liga- 

 ment to the plantar surface of the foot, where it is inserted into the tuberosity of the 

 scaphoid bone, sending prolongations to all the other tarsal bones, except the astra- 

 galus, and to the bases of the second, third, and fourth metatarsals. 



Nerve-Supply. — By the posterior tibial nerve from the fourth and fifth lumbar 

 and first sacral nerves. 



Action. — To extend the foot and to slightly invert the sole. 

 Relations. — The posterior tibial is the deepest muscle upon the posterior sur- 

 face of the leg. It is covered by the soleus and by the flexor longus digitorum, and 

 has resting upon it the upper portion of the posterior tibial and peroneal vessels (Fig. 

 617). The anterior tibial vessels pass through the interosseous membrane immedi- 

 ately above the origin of the muscle. A bursa sometimes intervenes between its 



tendon and the tuberosity of 

 Fig. 622. the scaphoid bone, and the 



tendon usually contains a ses- 

 amoid cartilage or bone where 

 it passes over the head of the 

 astragalus. 



Variations. — A portion of the 

 muscle is sometimes inserted into 

 the internal annular ligament. 



A muscle, which has been 

 called the peroneo-tibialis, not in- 

 frequently extends across between 

 the fibula and tibia, immediately 

 beneath the tibio-fibular articula- 

 tion and above the anterior tibial 

 vessels as they pass towards the 

 front of the leg. It is usually ru- 

 dimentary, but may form a well- 

 marked triangular sheet. 



2. Flexor Accessorius 



(Fig. 628). 



Attachments. — The ac- 

 cessory flexor of the toes (m. 

 quadratus plantae) arises by two heads from the medial and inferior surfaces of the 

 calcaneum and, passing distally, is inserted into the tendon of the flexor longus 

 digitorum. 



Nerve-Supply. — By the external plantar nerve from the first and second sacral 

 nerves. 



Action. — By acting on the long flexor tendons, to flex the second, third, fourth, 

 and fifth toes, and to counteract the oblique pull o*' the long flexor. 



The flexor accessorius, although apparently located entirely in the foot, is, nevertheless, a 

 crural muscle, since the tendon of the flexor longus digitorum, into which it is inserted, repre- 

 sents, as has already been pointed out, a portion of the plantar aponeurosis. Into this many 

 of the muscles of the leg were primarily inserted, and the accessorios represents the most distal 

 portion of the original deep sheet of the crural musculature. 



Vastus internus 



Inner condyle 



Insertion of 

 semimembranosus 



Vastus externus 



Popliteal surface of femur 

 External condyle 



Cut edge of capsular 



ligament 

 Long external 

 lateral ligament 



Short external 

 lateral ligament 



Popliteus 



Interosseous membrane 



Fibula 



Deep dissection of leg, showing popliteus muscle. 



