326 SYNOVIAL ENLARGEMENTS. 



touch, and accompanied with more or less Lameness, indicating 

 sprain, or other injury of underlying structures. In the former 

 instance, the affection seldom impairs the usefulness of the animal 

 and is generally the effect of premature overwork, or of a defective 

 shape of the joints, which is frequently due to hereditary pre- 

 disjDOsition ; and the swelling is soft, fluctuating, and cool. In 

 the latter, the injury is always serious, and demands complete 

 rest. I would not regard a bog spavin in an aged horse as an 

 unsoundness, if it was free from any inflammatory symptom, was 

 of moderate size, and was unaccompanied by lameness. 



Thoroughpins usually accompany large bog spavins, because 

 the distended capsular ligament of the latter tends to push up 

 the bursa of the perforans tendon out of its place. 



See " General Treatment/' p. 323, and remarks on drawing off 

 the fluid. 



Windgall below the Hock. 



I am entirely at a loss to give an apt and popular name to this 

 condition (Figs. 133 and 134), which is, anatomically speaking, 

 dropsy of the bursa of the peroneus tendon. It is a very rare 

 affection among English, Colonial, and Eastern horses; although 

 it is not, I believe, unfrequent among Continental horses that 

 have undergone a " school " training, in which excessive " col- 

 lection" is demanded. It does not appear to diminish the use- 

 fulness of the animal. In a case of a steeplechase horse which 

 I was training, and which had a windgall of this kind on each 

 hind leg, these enlargements gradually disappeared after I had the 

 animal in work for about a month. 



Thoroughpin 



appears as a swelling at the back of the hind leg, just above 

 the point of the hock, and in front of the tendons (the ham- 

 string) which are attached to that part (Figs. 135 and 136). When 

 pressed with the finger at one side of the limb, it will bulge out 

 with increased prominence on the other side ; hence the name. 



ANATOMY. — It is a distended condition of the synovial sheath which 

 surrounds the perforans tendon as it passes over the os caleis (Fig, 98). The sac 

 thus formed is pushed up into the space between the perforans tendon and the 

 tendo Achillis, which is the name given to the tendons that pass down to the 

 point of the hock. 



As in bog spavin, many horses are predisposed to thoroughpin 

 by defective shape, which, as a rule, is inherited. 



