LAMENESS IN THE HIND LEG 247 



above the inner tibial malleolus and extends about one-fourth 

 of the way down the metatarsus. The posterior part of the 

 capsular ligament of the hock joint is very thick in its most 

 dependent portions and is in part cartilaginous, forming a suit- 

 able groove for the passage of the deep flexor tendon. 



Etiology and Occurrence. — Strains and sequellae to debili- 

 tating: diseases constitute the usual causes of this affection. As 



Lz^y 



Fig. 57— Thoroughpin. Showing distension of tlie sheath of the deep flexor 

 tendon as it protrudes antero-externally to the fibular tarsal bone (cal- 

 caneum). 



a result of acute synovitis a chronic synovial distension of the 

 tarsal sheath occurs. Bog spavin is often present in case of 

 thoroughpin but the two conditions are separate and distinct 

 excepting in that both may occur simultaneously and as the 

 result of the same cause. Some animals are undoubtedly pre- 

 disposed to disease of synovial structures. The average horse 

 that has been subjected to hard service on pavements or hard 

 roads at fast work suffers synovial distension of bursae, thecae 

 or of joint capsules. Some of the well bred types such as the 



