n, pl  triceps  also  tri*ceps*es  :  a muscle that arises from three heads:  a  :  the large extensor muscle that is situated along the back of the upper arm, arises by the long head from the infraglenoid tubercle of the scapula and by two heads from the shaft of the humerus, is inserted into the olecranon at the elbow, and extends the forearm at the elbow joint - called also triceps brachii   b  :  the gastrocnemius and soleus muscles viewed as constituting together one muscle - called also triceps surae  .
 
 
 
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