38 THE HORSE IN MOTION. 



to its functions in locomotion. The words "adductor" and "abduc- 

 tor," meaning tlic function of drawing to or away from the vertical 

 plane passing through the axis of the body, are well enough, but we 

 must not be misled by the application of these names to muscles which 

 may have such action to the extent only of five per cent of their work, 

 and the rest, or eighty-five per cent, devoted to propulsion. 



I have already referred to the misnomers in muscles ; they mislead 

 the mind no less with regard to their action than to their form and 

 construction. What can be more inappropriate than the names semi- 

 membranosus and semi-tendinosus, meaning half membrane and half 

 tendon, when applied to the muscles so named in the horse ? They 

 are well enough wiien applied to the corresponding muscles in man, 

 but in the horse they are not at all membranous or tendinous. 



We should be glad to dispense with names altogether, and apply 

 abstract or algebraic terms to avoid misconceptions, if practicable, but 

 we must use such as are given, and, where there are synonymes, use 

 such as are least liable to the objection referred to. 



There is a group of muscles whose action is to advance the wliole 

 posterior extremity after the act of propulsion is complete. They are 

 all deep-seated, with two exceptions. 



The. psoas magnns (Plates VI., VII., a, a) has its origin in the abdo- 

 men, along the under sun'ace of the lumbar vertebra ; its fibres, which 

 determine the course of its action, are directed backward and down- 

 ward, and it terminates in a long tendon which is inserted into a rough 

 ridge on the inner side of the femur, or thigh bone, just below the head 

 of the bone; another of this group is the iliacus (e, Plate VII.), which 

 arises from the lower face of the ilium, or hip. The course of its fibres 

 is similar to that of those of the psoas, but its origin being farther from 

 the median plane, its direction is more inward to join the last-named 

 muscle at the same point on the inner face of the fenuir. These two 

 muscles are of delicate organization, and, though differing in form, unite 

 in their function of flexing the femur upon the pelvis, and so carr3'ing 

 the whole leg forward. The iliacus, having its course more inward 

 than the other, has the effect of carrying the free end of the femur out- 

 ward, — the "stifle action," so important in the trotting horse. 



