THE OBTURATOR NERVE 171 



This nerve supplies the muscles which lie on the back of the tibia, 

 so that we have inability of these muscles when the nerve is paralysed. 

 The result is that the animal cannot extend the hock, owing to the 

 inaction of the gastrocnemius and flexor perforatus muscles. Neither 

 can he flex the fetlock and interphalangeal joints, since the flexor acces- 

 sorius, flexor perforatus, and flexor perforans are involved. 



In the resting condition, then, the foot is placed flat on the ground. 

 The gastrocnemius and flexor perforatus being relaxed, the hock is let 

 down to a much lower level than that of the opposite limb, and as the 

 flexor metatarsi is active the hock does not become unduly extended, as 

 in paralysis of the nerves supplying the anterior tibial region. The 

 result is that the inferior end of the metatarsal bone becomes pressed 

 forwards and there is "knuckling " at the fetlock. 



If the patient is caused to move, all the joints are excessively flexed 

 and the foot is raised abnormally high, giving an appearance not unlike 

 stringhalt. The foot is set down flat when the flexors relax, without 

 any force. 



The above symptoms may be deduced from an anatomical study ol 

 the nerve. Moller recorded a typical case, and also proved that by 

 experimentally dividing the nerve as it passes between the two heads 

 of the gastrocnemius, the symptoms presented are coincident with 

 destruction of the function of the nerve 



THE OBTURATOR NERVE 



This is another large nerve. Its fibres are derived from the fourth 

 and fifth lumbar roots of the plexus, and the nerve leaves the plexus 

 between the anterior crural nerve and the trunk which connects the 

 anterior and posterior divisions. 



It passes above the external iliac artery, and is then seen to be 

 covered only by the peritoneum. Passing to the inner side of the 



