AS TO SOUNDNESS. 133 
not to be distinguished from “causticking” badly per- 
‘formed, or the blow from another horse. If hocks have 
been well fired, not too early in life, they are far less 
likely to become lame from spavin than those which 
have not been treated at all. 
Spavins situated very far back on the hock I have 
never known to produce lameness. I have again and 
again passed such, and have never had occasion to 
regret it. Perhaps you had better mention it in your 
certificate; or what is better, write a note with your 
certificate and let your employer know you have not 
overlooked the fact. 
Bog-spavin is one of the most wretched terms in our 
nosology. It used to be called blood-spavin, from an 
error in observation. You know the true hock joint 
is a very large joint, and the bag, bursa, or purse which 
secretes and contains the oil for its lubrication, is apt 
to secrete and therefore to contain a little more oil than 
js perhaps needful, and when this is so the bursa is dis- 
tended and tense. A very large vein, called the saphena 
vein (from the Greek ca¢#s, manifest or conspicuous), 
passes directly over it and close to it and between it 
and the skin. So that when the bursa distends, it 
presses upon this vein and distends it, and makes 
it more conspicuous; hence the older anatomists, with 
the feeble light of their day, thought that it was the 
bursting of this vein into the joint which caused the 
distended bursa, and so they named it blood-spavin. 
It afterwards came to be known as bog-spavin, on 
