A flexor directs an appendage forward; an exception is the gastrocnemius in this part of the leg
In mammals, however, the equivalent long flexor, gastrocnemius, 
inserts on a new ... Tetrapods, with the exception of mammals, utilize part of the 
constrictor... [DOC] [TLE] Download PDF - Springer [PAR] appendages either to counteract or to strengthen the effect of external forces.