THE MUSCLES OF THE LEG AND FOOT 339 



tendinosus, semimembranosus, and adductor, (below) the fascia and skin; laterally 

 (above), the biceps femoris and peroneal nerve, (below) the fascia and skin. The 

 popliteal lymph lands lie on the upper part of the muscle. 



Blood-supply. — Popliteal artery. 



Nerve-supply. — Tibial nerve. 



2. Soleus (Fig. 296).— This muscle is very small in the horse. It lies along 

 the lateral border of the gastrocnemius under the common deep fascia, on the prox- 

 imal half of the lateral surface of the leg. 



Origin. — The head of the fibula. 



Insertion.— The tendon of the gastrocnemius, about the middle of the leg. 



Action. — To assist the gastrocnemius. 



Structure.— It is a thin, fleshy band, usually about an inch (ca. 2 to 3 cm.) in 

 width, and terminates on a thin tendon which fuses with that of the gastrocnemius.^ 



Relations. — Superficially, the skin, fascia, and peroneal nerve; deeply, the 

 lateral extensor and deep flexor. 



Blood-supply. — Posterior tibial artery. 



Nerve-supply. — Tibial nerve. 



3. Superficial digital flexor (M. flexor digitalis pedis superficialis) (Figs. 292, 

 296, 297). 2 — The proximal part of this muscle lies between and under cover of 

 the two heads of the gastrocnemius. It consists almost entirely of a strong tendon, 

 the belly being very little developed. 



Origin. — The supracondyloid fossa of the femur. 



Insertion. — (1) The tuber calcis; (2) the eminences on each side of the prox- 

 imal extremity of the second phalanx, and the distal extremity of the first phalanx 

 behind the collateral ligaments of the pastern joint. 



Action. — To flex the digit and extend the hock joint. On account of the ex- 

 ceedingly small amount of muscular tissue the action is to be regarded chieflj^ as a 

 mechanical effect which results from the action of other muscles on the stifle joint. 



Structure. — The origin is by means of a strong round tendon which is incom- 

 pletely covered with fleshy fibers as far as the upper third of the leg. Here it is 

 intimately attached to the gastrocnemius, especially to the lateral head. At the 

 distal third of the tibia it winds around the medial surface of the gastrocnemius 

 tendon, and then occupies a position behind the latter. At the point of the hock 

 it widens out, forming a sort of cap over the tuber calcis, and detaches on either side 

 a strong band which is inserted into the tuber calcis with the tarsal tendons of the 

 biceps and semitendinosus. It then passes downward over the plantar ligament, 

 becomes narrower, and is arranged distally as in the thoracic limb. A large syno- 

 vial bursa (B. calcanea subtendinea) lies under the tendon from the distal fourth of 

 the tibia to the middle of the tarsus. A subcutaneous bursa (B. calcanea subcu- 

 tanea) is sometimes present on the wide part of the tendon at the point of the hock. 



Relations. — Posteriorly, the gastrocnemius, fascia, and skin; anteriorly, the 

 femoro-patellar capsule, the popliteus, the deep flexor, and the popliteal vessels; 

 medially, the tibial nerve. 



Blood-supply. — Posterior femoral artery. 



Nerve-supply. — Tibial nerve. 



4. Deep digital flexor (M. flexor digitalis pedis profundus) (Figs. 292, 298).^ — 

 The belly of this muscle lies on the posterior surface of the tibia, and is divisible 

 into three heads, which, however, finally unite on a common tendon of insertion. 



Origin. — (1) The posterior edge of the lateral condyle of the tibia; (2) the 

 border of the lateral condyle of the tibia, just behind the facet for the fibula; (3) 



iThe soleus is sometimes included with the two heads of the gastrocnemius under the 

 name triceps surae. 



2 This is also known as the flexor pedis perforatus or superficial flexor of the phalanges. 

 ' This muscle is also commonly termed the flexor pedis perforans. 



