DISLOCATIONS 349 



can be remedied. The cases referred to, in most instances, depend on 

 the perforatus and its outer dense fibrous membrane, extending from 

 the superior part of the sesamoid bones to where the tendon becomes 

 inserted into the supero- posterior part of the os coronte, and whicli 

 is continuous with the fibrous frog, becoming more or less thickened, 

 and sometimes semi - cartiLaginous ; consequently they are shortened at 

 this particular part. Taking a view of the anatomical relationship of 

 these structures, forming as they do a synovial sheath for the perforans, 

 and also their pathological condition, we should not be justified in 

 using the scalpel, especially as the oidy chance of eft'ecting our object 

 would be by operating below the fetlock -joint, and this we should not 

 be warranted in doing." — Varnell. 



ACCIDENTAL DISLOCATIONS 



Accidental dislocations are as numerous almost as the joints them- 

 selves; horses, by the nature of their employments and the dangers to 

 which they are exposed, incur injuries which dislocate and damage the 

 joints of the limbs, and less frequently those of the spine and other 

 parts of the skeleton. The liability to dislocation is much greater in 

 some joints than in others. This depends partly on the form and 

 character of the joint itself, and partly also on the strength of the 

 ligaments and muscles which unite and support it. The rarity of 

 dislocation of the hip is due to the depth of the cup into which the head 

 of the femur fits, and the strength of the ligaments and muscles whicli 

 bind them together. The relative frequency of luxation of the patella 

 may be ascribed to the facility with which the bone is under some cir- 

 cumstances enabled to glide over the outer small ridge of the femur 

 upon which it plays. 



Luxation of certain bones, notalily the patella, is sometimes due to 

 extreme debility and weakness, while in others it follows upon contraction 

 of the tendons induced by hard W'ork, sprains, and other injuries, flmiiliar 

 examples of which are to be seen every day in our streets. " Upright" 

 is the term used to denote such cases of partial dislocation occurring in the 

 region of the pastern; l)ut they are not infrequently seen in a condition in 

 which the lower extremity of the canon-bone projects beyond the level of 

 the articular surface of the suffraginis, or upper pastern-bone. 



