272 THE EXTERIOR OF THE HORSE. 



elongated, cylindrical tumor, ordinarily ot a small volume, and about ten centi- 

 metres in length. This is called calcanecm hygroma. 



H. Bouley observed vidth justness that the synovial cul-de-sac which permits 

 the gastrocnemius tendon to glide upon the summit of fehe calcaneus, during 

 the movements of extensive flexion, is so powerfully supported by the expansion 

 of the perforatus that it is absolutely impossible for it to dilate in the form of 

 external enlargements. He adds, with equal accuracy, that this synovial cannot 

 in any manner give rise to the tumor which we have studied above under the 

 name of capped hock. 



Finally, it is also possible to meet hydropsy of the small bursa which facili- 

 tates the gliding of the cunean tendon of the flexor of the metatarsus over the 

 surface of the internal lateral ligament. It presents a small, soft, fluctuating 

 tumor of the size of a large bean, situated in front of the point where the exos- 

 tosis of a spavin usually forms and for which it is sometimes mistaken. This 

 dilatation has received the name of cunean hygroma, on account of its location 

 in relation with the tendinous branch under which it is developed. 



d. Articular Synovials. — It is rather common to meet upon the astrag- 

 aloid pulley and in the corresponding grooves of the tibia more or less deep 

 multiple striae or fissures, perfectly regular, and all of them parallel to the lips 

 of the astragalus. These strice of the articular surfaces are most common in old 

 horses. They are, without dpubt, due to some slow and obscure irritation of the 

 tibio-tarsal joint, and correspond probably to a special irregularity of its move- 

 ments ; but clinicians at present have not determined in a precise manner the 

 external symptoms of this variety of lesions, which should consequently be 

 investigated. (See Defects of the Gaits : String-halt.) 



The most serious alteration of the tibio-astragaloid articulation is consecutive 

 to a hydropsy of its synovial membrane. The synovia, under the influence of an 

 excessive functional activity on the part of this membrane, is secreted in larger 

 quantity in the articular cavity, and, in the long run, exercises pressure from 

 within which, little by little, dislocates the parietes of the articular cavity. But 

 as the latter are not equally sustained everywhere, the places which ofter the 

 least resistance to the internal pressure are distended beyond their physiological 

 limits and produce a hernia, by forming under the skin three tumors whose posi- 

 tion is stationary, whose volume and tension alone change according to the 

 intensity of the alteration. These three tumors constitute what is called articular 

 thorough-pin of the hock. 



The first of these is located in the fold of the hock and a little to the internal 

 side. It modifies the profile of the anterior face of this region by the presence 

 of an abnormal curve, yielding, and always more tense to the finger when the 

 member is on the ground. 



The other two articular dilatations are situated behind and above the lateral 

 ligaments, between the tibia and the perforans tendon. They have a variable 

 volume, which ranges from that of a walnut to that of a child's head; the 

 internal is most frequently larger than the external, which is sometimes absent. 

 The presence of one of these constantly coexists with that of the anterior swell- 

 ing, and that is what we might expect, since all three are only diverticula of the 

 same cavity. Pressure exercised upon one of them is communicated to the 



others. 



The synovial dilatations are, in general, less grave than the osseous tumors. 



