erection, penis

erection, penis

the hardening and lengthening of the mammalian penis in order to bring it into condition for copulation. An erection is brought about by engorgement of blood in the CORPUS SPONGIOSUM and CORPUS CAVERNOSUM, causing them to become swollen and rigid.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005