AS TO SOUNDNESS. 137 
the back of the tibiz, and so unduly press upon the 
synovial sheath. In these cases the very least increase 
of the oil in the sheath is shown. Where the hocks 
are bent, and this lubricating sheath is not unduly 
pressed between the os calcis and the back of the tibia 
from their being well apart, should there be a large 
thoropin, then the sheath must be much distended ; and 
this is very likely owing to some injury to the tendon 
of the flexon pedis perforans, which in bent hocks has 
necessarily more stress thrown upon it. You will do 
well to reject such as unsound. There are other ap- 
pearances similar to thoropin, of which the most common 
is bog-spavin, showing itself at the back- of the joint as 
well as in front, in which case unsoundness must be 
your verdict, as it indicates a grave defect somewhere in 
the joint. 
Curb is a disease due to strain upon the back of the 
hock when the hind-foot is advanced far under the body, 
as in the rearing and momentary poise during the pre- 
paratory act of leaping a height, and in other conditions 
such as fast trotting. The hocks may be so bent as to 
protrude the feet beneath the body during ordinary 
movement, in which case liability to curb is great. The 
liability to curb is greatest, however, in “ curby’’ hocks ; 
hence the name. “Curby” hocks may or may not be 
the subjects of curb. If they are free, no one can tell 
how long they will remain so. <A “curby” hock is an 
extremely defective hock, having its front lower bones 
small, also the head of the large metatarsal small, and 
