Cremaster is a muscle covering the spermatic cord and testes. It is a derivative of the internal oblique muscle as the spermatic cord passes from the abdomen to the scrotum.
It originates from the muscle fibres beyond the level of the deep ring of the inguinal canal. It forms the middle covering layer of the spermatic cord as it passes through the canal and distally to the tunica vaginalis.
Cremaster acts to retract the testes. This functions to keep the testes warm and protect from injury. The cremasteric reflex is a clinical test of the muscle.
It is innervated by the genital branch (L2) of the genitofemoral nerve (L1,2).