158 HEREDITARY DISEASES OF HORSES AND CATTLE. 
feet of horses of this character changed into bone at four and 
five years old. The reason of this is evident enough : con- 
cussion is easily produced in the joints of the character of 
horses described; inflammation of a slow chronic kind fol- 
lows as a natural consequence, and osseous effusion is the 
result. 
There is no difficulty in establishing the hereditary cha- 
racter of those diseases. Taking spavin as an example, we 
have numerous and unquestionable cases to produce. Some 
ten or dozen years since a spavined thorough-bred stallion 
served mares in the neighbourhood of Truro, and in a few 
years afterwards it was really astonishing to see the number 
of his stock that were similarly diseased. One striking cir- 
cumstance connected with this horse is much to the purpose. 
A half-bred mare, one of his stock, exhibited spavins at four 
years old, and, becoming unfit for fast work, was kept for 
breeding purposes and occasional work on the farm. Two 
of this mare’s stock also exhibited spavins in a short time 
after the breaking. 
There is a curious case recorded in the Veterinarian , by Mr. 
Percivall, of a thorough-bred horse called (i Dominie Samp- 
son,” that had run very successfully on the English turf, and, 
although fired in both hocks, was inconsiderately purchased 
for the East India Company, and sent out as a covering stal- 
lion to the stud at Buxar , where for four years he had forty 
mares annually, and the whole of which generally proved 
with foal, but were affected either with curbs or spavins, and 
only one of his stock was passed into the cavalry : conse- 
quently he was discarded from the stud. 
(b.) Curbs are frequently found in horses exhibiting the 
character of hock described in the last example, and are 
generally caused by injury of the annular ligament, from over 
exertion, producing swelling and inflammation about three 
inches below the point of the hock formed by the os calcis . 
The peculiar form of this bone appears to be connected with 
the cause of the disease. Its chief purpose is to act as a 
lever for the action of very powerful muscles, the tendons of 
which are inserted into its extremity, and in proportion to 
the projection of this bone will the muscular energy be in- 
creased by which the joint is moved. On this account, its 
length is a matter of considerable importance. It is sup- 
posed also to assist indirectly in supporting the superincum- 
bent weight with the other bones of the hock, and materially 
assists in preserving these parts from the effects of concussion. 
But when the os calcis is short, forming a short pointed hock, 
the leverage or mechanical power is injuriously diminished, 
