30 THE SURGICAL ANATOMY OF THE HORSE 



line the flexor perforatus, which arises from the supracondyloid fossa 

 of the femur and which plays over the back of the stifle joint, will 

 be observed. Behind the flexor perforatus again there are two large 

 muscles. These are the outer and inner heads of the gastrocnemius. 

 The outer head arises from the outer lip of the supracondyloid crest. 

 At the level of the section the two heads will be observed to come 

 into apposition with each other in the median line, and a little lower 

 down they become united to one another. 



Near the anterior border of the outer head of the gastrocnemius, 

 and placed superficially between the outer aspect of the muscle and the 

 deep layer of fascia, is the external popliteal nerve. This is one of the 

 branches of the great sciatic nerve, which it leaves soon after the latter 

 emerges from the greater sacro-sciatic foramen. The external popliteal, 

 in turn, divides into the anterior tibial and musculo-cutaneous nerves a 

 little below the level of the section. 



The internal popliteal nerve will be observed to lie on the anterior 

 aspect of the inner head of the gastrocnemius. This nerve is directly 

 continued as the posterior tibial nerve, which lower down the limb 

 emerges from beneath this muscle and becomes ultimately split up into 

 the external and internal plantar nerves. 



Other structures are represented in the Plate which have compara- 

 tively little surgical importance. 



Plate Vni. represents a transverse section at the seat of posterior 

 tibial neurectomy [i.e., 5.5 inches above the summit of the tuber calcis). 

 The section is one of the left limb. 



In the middle of the Plate, but towards the inner side, is observed 

 the tibia. The outline of the bone here in section, is peculiar, its inner 

 aspect being rounded, whilst outwardly it is drawn out to a point. This 

 indicates the edge to which the tibio-fibular interosseous membrane is 

 attached. 



Lying on the anterior face of the bone we have a large, transversely 

 elongated muscular mass. This is the flexor metatarsi, the muscular 



