when examining the scrotum in a young male child test the cremasteric reflex by
Cremasteric reflex This reflex is elicited by lightly stroking or poking the superior and medial (inner) part of the thigh - regardless of the direction of stroke.[1] The normal response is an immediate contraction of the cremaster muscle that pulls up the testis ipsilaterally (on the same side of the body). The reflex utilizes sensory and motor fibers from two different nerves. When the inner thigh is stroked, sensory fibers of the genitofemoral nerve are stimulated. These activate the motor fibers of the genital branch of the genitofemoral nerve which causes the cremaster muscle to contract and elevate the testis. [2] :262
Sexual differentiation in humans The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote.[3] Females have two X chromosomes, and males have a Y chromosome and an X chromosome. At an early stage in embryonic development, both sexes possess equivalent internal structures. These are the mesonephric ducts and paramesonephric ducts. The presence of the SRY gene on the Y chromosome causes the development of the testes in males, and the subsequent release of hormones which cause the paramesonephric ducts to regress. In females, the mesonephric ducts regress.