324 SYNOVIAL ENLARGEMENTS. 



generally the effect of premature overwork, or of a defective shape 

 of the joints, which is frequently due to hereditary predisposition ; 

 and the swelling is soft, fluctuating, and cool. In other cases, the 

 distension is at first hard, painful to the touch and accompanied 

 with more or less lameness, indicating sprain, or other injury of 

 underlying structures. This 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, 

 of moderate size, and 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. 321, 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 infrequent among Continental horses that have undergone 

 a " school " training, in which excessive " collection" is demanded. 

 It does not appear to diminish the usefulness of the animal. In a 

 case of a steeplechase horse I was training, which had a windgall 

 of this kind on each hind leg, these enlargements gradually dis- 

 appeared after I had the animal in work for about a month. 



Thoroughpin. 



This appeal's as a swelling at the back of the hind leg, just above 

 the point of the hock, and in front of the tendons (the hamstring) 

 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 calcis (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. 



Thoroughpin, like bog spavin, is often unaccompanied by in- 

 flammatory symptoms, and is then of little moment. When, how- 



