Corpus cavernosum penis

one of a pair of sponge-like regions of erectile tissue, which contain most of the blood in the penis and clitoris during an erection

The corpus cavernosum penis (or corpus cavernosum urethrae) is one of two sponge-like sections of tissue in the male penis. They contain most of the blood during an erection. The term literally means "cave-like body"

Corpus cavernosum penis
Transverse section of the penis.
The constituent cavernous cylinders of the penis.
Latincorpus cavernosum penis
Anatomical terminology

Process change

The corpus cavernosum are placed along the length of the penis. They are found along the penis shaft, from the pubic bones to the head of the penis. The spongy tissue fills with blood. The blood comes from arteries down the length of the penis. The blood fills the corpora cavernosa. This causes it to swell. When swollen, it holds 90% of the blood involved in an erection. This increases both the length and circumference of the penis.

Blood can leave only through a system of veins around the outside wall of the corpus cavernosum. The expanding tissue constricts these veins. This preventing blood from leaving. The penis becomes rigid as a result.