52 PRINCIPLES OP VETERINARY SCIENCE 



1. Gliding, the simplest and only movement possible between 

 two plane or undulating facets. 



2. Flexion, which brings two bony pieces nearer each other by 

 closing the angle more or less. 



3. Extension, the reverse movement by which the bones are 

 straightened on each other. 



4. Adduction, which brings the inferior end of the movable 

 bone toward the median plane of the body. 



5. Abduction, where it has the opposite effect. 



6. Circumduction, in which the shaft of the distal bone of the 

 joint describes the surface of a cone. 



7 Rotation, in which one bone pivots or rotates on the other. 



DESCRIPTIONS OF IMPORTANT JOINTS 



The shoulder, fetlock, pastern, and coffin joints of the fore 

 leg; and the hip, stifle, and hock joints of the hind leg are the 

 most important, for they are largely concerned in the mechanism 

 of locomotion. As we have already learned about the shape of 

 the articular surfaces of the bones which enter into these joints, 

 it will not be necessary to describe them again. 



The hip-joint of the horse in addition to the usual articular 

 cartilages has an accessory cartilage which plays an important 

 part in its work. It is in the form of a marginal ring of fibro- 

 cartilage, which very appreciably deepens the acetabulum and 

 makes dislocation extremely difficult if not impossible. The 

 articulation is of the ball- and socket-type and is capable of all 

 the movements just described except gliding. 



The stifle joint of the horse is the largest and most elaborate 

 of all the articulations. Its synovial sac is the largest found in 

 any joint. This is because it comprises two joints, the femoro- 

 patellar and the femorotibial. Two C-shaped accessory cartilages 

 are placed between the femur and tibia to adapt them more prop- 

 erly to each other. Two strong rounded cruciate ligaments bind 

 the femur to the tibia. The principal movements of the stifle 

 are flexion and extension (see Fig. 75). 



The hock- joint of the horse is another complex and important 



joint. On it the strain of propulsion chiefly falls and the jar 



which results from concussion during the act of progression is 



largely broken. The movements are confined mostly to flexion 



and extension. When the animal moves the joint opens and 



closes simultaneously with the stifle. „_ 

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