SPAVIN. 
721 
and between the cuneiform and metatarsus. This anchylosis may either 
be true or false. The ligaments are then often ossified, and so surrounded 
by new growths of bone that they can scarcely be recognised. Some¬ 
times the sheath of the flexor metatarsi muscle becomes diseased. Petit 
states never having found this part of the hock-joint diseased even when 
extensive exostoses existed. 
In many cases pathological processes are confined to the lower and 
inner portions of the hock, though not infrequently they extend further, 
seize on the cuneiform bone and head of the inner small metatarsal, or 
even on the astragalus and external surface of the joint. The French, 
therefore, distinguish “ eparvin tarso-metatarsien,” as opposed to the 
disease of the cuneiform bones and metatarsus, which is termed 
“ eparvin metatarsien.” 
The appearance of the above-described changes, either alone or in 
combination, is easily explicable on the theory that the point of origin of 
the disease varies. Menveux made a collection of hocks, showing widely 
varying anatomical changes, from horses, all of which had clinically been 
recognised as suffering from “ spavin.” 
Causes. In no other disease is the division of causes into causa 
externa and causa interna so well warranted and so practical as in 
spavin. The causa interna is a predisposition partly dependent on the 
conformation of the hock, partly on that of other portions of the body. 
Whilst the complicated mechanism of the hock predisposes to disease, 
and especially to inflammation, this tendency is enormously increased 
by defective formation of the joint. It is scarcely needful to say that, 
under the powerful action of the muscles of the hind limb, small, cramped 
joints are more likely to suffer than those having well-developed, broad 
and ample articular surfaces. Defective development of the lower 
portions of the hock and of the upper end of the metataisus, the 
condition described by horsemen as “ tied-in hock,” is particularly 
disastrous, while a distinct curvature (sickle-shaped hock) is almost as 
bad. In this formation the action of the extensor muscles of the hind 
limb produces excessive movement of the hock-joint and great pressure 
on the articular surfaces, with danger of injury to the ligaments of the joint. 
But these visible peculiarities of formation are not the sole causes 
of spavin: the intimate structure of the bones and ligaments may 
predispose to disease, as shown by the inheritance of spavin, and its 
occurrence in entire strains, whose hock-joints appear perfectly foimed. 
This view is further supported by the rare occurrence of disease in some 
races, like the Danes and Holsteiners, whose hocks are by no means 
irreproachable. In breeding, therefore, special attention should be 
paid to this disease. The exact nature of the predisposition at present 
eludes us, though by many it is considered to result from incomplete 
