84 ANATOMY OF THE WOOD RAT 



mediad, between the astragalus and ankle to the sole, 

 where it thickens before dividing, usually into five branches, 

 one of which extends to the terminal phalanx of each digit. 

 In a minority of the specimens examined of all three sub- 

 genera there were but four branches extending respectively 

 to the four lateral digits. 



M. tibialis posticus (figs. 7, 32, 33) has origin from the 

 proximal portion of the lateral border of the medial ridge, 

 chiefly deep to the flexor longus. The fibers are pennated 

 onto its tendon, which passes over the medial ankle and is 

 inserted onto the sesamoid bone of the tarsus. 



The innervation of these eight flexors of the calf is by 

 means of the tibial nerve. 



The extensor group of the lower leg includes but three 

 muscles, as follows: 



Mm. tibialis anticus 

 extensor hallucis 

 extensor digitorum longus 



M. tibialis anticus (figs. 6, 7, 17, 18, 32, 33) originates 

 from the cranio-lateral border of the head of the tibia; by 

 aponeurotic fibers from the fibular collateral Hgament of 

 the knee; and from the fascia covering the proximal por- 

 tion of -the tibial shaft. The fibers of the latter portion 

 are pennated upon the ental surface of the broad tendon 

 which develops within the muscle. The distal tendon 

 passes beneath the transverse ligament of the instep to 

 the medial border of the pes and is inserted upon the ento- 

 cuneiform bone. 



M. extensor hallucis (figs. 6, 18, 32) is a very slender 

 muscle lying between the tibialis anticus and extensor 

 digitorum longus. It arises from the interosseous fascia 

 between the tibia and fibula rather than from the border of 

 the latter bone. Its feeble tendon passes beneath the 

 transverse and crural hgaments in close relation with the 

 tibialis anticus, and is inserted upon the dorsal aspect of 

 the hallux. 



