The cells of the cortex arise from the coelomic epithelium that lies on the angle between the developing gonad and the attachment of the mesentry. The cells arising from the coelomic epithelium may be divided into two groups.

a) The cells that are formed first are large and audophilic. They surround the cells of the medulla and form the fetal cortex. The fetal cortex disappears after birth.

b) Subsequently the coelomic epithelium gives origin to smaller cells that surrounds the fetal cortex. These smaller cells forms the definitive cortex.

The cells of the medulla are derived from the neural crest. They are similar to the post ganglionic sympathetic neurons. Preganglionic sympathetic neurons terminate in relation to them. These cells migrate to the region of the developing cortical cells and come to be surrounded by them.