i68 THE SURGICAL ANATOMY OF THE HORSE 



sive cavity consisting of several divisions. ... As the abscess cavity 

 closed the diiiiculty in movement gradually diminished, though the gait 

 for long remained uncertain, especially when the horse was on uneven 

 ground, the phalanges failing to be extended and the animal ' knuckling 

 over' at the fetlock. 



" There can be no doubt that the abscess originated in the paraproctal 

 connective tissue, in consequence of infection from the rectum. It then 

 extended between the muscles of the quarter and pressed on the great 

 sciatic nerve, so that both the external and internal popliteal nerves were 

 affected. The symptoms due to injury to the external popliteal were 

 more marked because the function of those muscles supplied by the 

 internal popliteal (gastrocnemius, flexor perforans, perforatus, &c.) was 

 partially replaced by their tendinous apparatus ; this explains why weight 

 could still be borne on the limb." 



In 1899 the author saw a somewhat similar case of paralysis of the 

 great sciatic nerve in a two-year-old short-horn bullock, which had been out 

 to pasture and had not been seen by the owner for several months; conse- 

 quently there was no evidence as to the length of time the animal had been 

 lame. The position of the abscess was evident the first time the animal 

 was seen by the writer, for there was an enormous swelling at the back 

 of the thigh. Upon exploration with a searching needle the swelling 

 was found to be due to the presence of an abscess some distance below 

 the cutaneous surface. The abscess was opened by separating the 

 hamstring muscles, and between two and three quarts of thick, offensive- 

 smelling pus escaped. The cutaneous opening was kept patent, and the 

 abscess cavity washed out frequently with antiseptic solutions. The 

 cavity thus filled up from the bottom. Lameness gradually disappeared, 

 and recovery was complete in three weeks. 



The position of the great sciatic nerve affords it protection against 

 external injury to such degree that it is difficult to see how paralysis 

 can occur from causes other than the pressure upon it of such growths 

 as abscesses or tumours which form along its course, 



