78 THE ANATOMY OF THE HORSE. 



the biceps and the outer head of the gastrocnemius, where, a little 

 behind the external lateral ligament of the stifle, it divides into the 

 musculocutaneous and anterior tibial nerves. 



The Musculo Cutaneous Nerve descends along the line of contact 

 of the extensor pedis and peroneus, supplying filaments to the latter 

 muscle. At the lower third of the leg, as has already been seen, the 

 cutaneous division of the nerve pierces the deep fascia, and passes over 

 the hock to supply the skin on the outer side of the metatarsus. 



The Anterior Tibial Nerve separates from the preceding at an 

 acute angle, and a few inches below the stifle it passes under cover of 

 the extensor pedis. It supplies twigs to the last-named muscle, the 

 flexor metatarsi, and the short extensor ; and descends at the outer 

 side of the tibial vessels, afterwards accompanying the large metatarsal 

 artery to terminate in the skin on the outer side of the digit. 



The Anterior Tibial Artery (Plate 19). This, it will be recollected, 

 is one of the terminal branches of the popliteal artery. Originating 

 behind the upper extremity of the tibia, it is here seen coming forwards 

 through the tibio-fibular arch. It descends on the tibia under cover of 

 the flexor metatarsi, and accompanied by the nerve and vein of the same 

 name. Gaining the front of the hock, it rests on the anterior tibio-tarsal 

 ligament, covered by the flexor metatarsi and extensor pedis at their 

 line of contact. Here it deviates outward under the tendon of the last- 

 mentioned muscle, and divides into two vessels of unequal size. The 

 larger of these, which continues the direction of the parent vessel, is the 

 large metatarsal artery ; the other is the perforating metatarsal artery ; 

 and both will be dissected with the metatarsus. The anterior tibial 

 artery gives off numerous unnamed muscular branches to the extensor 

 pedis, flexor metatarsi, and peroneus ; and articular branches to the hock. 



The Anterior Tibial Vein, which may be double, keeps close com- 

 pany with the artery. It is formed at the front of the hock by the 

 fusion of several rootlets. The largest of these is the upward continua- 

 tion of the deep metatarsal vein, which comes forwards through the 

 vascular canal between the tarsal bones. After passing backwards 

 through the tibio-fibular arch, the anterior joins the posterior tibial 

 vein to form the popliteal. 



THE METATARSUS AND DIGIT. 



The distal portion of the horse's hind limb, beyond the lower ex- 

 tremity of the tibia, is technically termed the pes, as it corresponds to 

 the foot of man. The tarsus, or hock, represents the human ankle ; 

 the part between the tarsus and fetlock corresponds to the body of the 

 human foot, and is termed the metatarsus ; while the rest of the limb, 

 beyond the fetlock, is the digit, and is the homologue of man's third toe. 



