340 FASCLE AND MUSCLES OF THE HORSE 
the middle third of the posterior surface and the upper part of the lateral border of 
the tibia, the posterior border of the fibula, and the interosseous ligament. 
Insertion—The semilunar crest and the adjacent surface of the cartilage of 
the third phalanx. 
Action.—To flex the digit and to extend the hock joint. | 
Structure —(1) The medial head is termed the long digital flexor (M. flexor 
digitalis longus s. flexor accessorius); it is easily isolated (Figs. 298, 584). It hasa — 
fusiform belly, which crosses the leg obliquely and lies in a groove formed by the 
Peroneus tertius 
Tibialis anterior 
Long digital 
extensor 
Cutaneous branch of 
saphenous nerve 
Superficial peroneal 
nerve 
Intermuscular. 
septum 
Lateral digital 
extensor 
a7—} Saphenous vessels 
Intermuscular and nerve 
septum Popliteus 
Flexor hallucis 
Flexor digitalis longus 
Tibialis posterior 
Vein 
Soleus 
Tibial nerve 
Lateral head of gastroc- E ee oe 
ete Superficial digital flexor 
Recurrent tarsal vein Medial head of gastroc- 
nemius 
Fic. 297.—Cross-section oF Lerr Lea or Horse. 
The section is cut about the junction of the proximal and middle thirds of the region. 1, Anterior tibial vessels; 
2, deep peroneal nerve; 3, fibula; 4, posterior tibial vessels; 5, recurrent tibial vessels. A cutaneous branch of the 
saphenous nerve is shown medial to the popliteus, but is not marked. 
other heads and the popliteus. This terminates near the lower third of the tibia 
on a round tendon which descends in a canal in the medial ligament of the hock, 
and joins the common tendon about a third of the way down the metatarsus. In 
its course over the medial surface of the hock the tendon is provided with a syno- 
vial sheath which extends from the distal fourth of the tibia to the junction with 
the principal tendon. (2) The superficial head is the tibialis posterior (M. tibialis 
posterior); it is only partially separable from the deep head. It has a flattened 
belly, terminating near the distal third of the tibia on a flat tendon which soon fuses 
