The penis enlarges every time an erection takes place.
The tunica albuginea is what stops the penis from expanding beyond a normal erection. The tunica is a fiber-elastic connective tissue consisting of two layers. The inner most layer of the tunica — called the inner circular layer — surrounds all three corpus chambers. Together the top two chambers make up the Corpus Cavernosa (CC). The bottom chamber holds the urethra, and is called the Corpus Spongiosum (CS). The outer layer of the tunica — the outer longitudinal layer — surrounds only the Corpus Cavernosa. In a nutshell, the tunica limits the size of the erect penis similar in the same manner that a bicycle tire limits the expansion of the inner tube inside.
What holds the penis in place? The penis ligaments. Ligaments are a sheet of tough, fibrous tissue that connect at a joint or support an organ. There are two main ligaments that support the penis: the fundiform ligament and the suspensory ligament. They are both located in the region of the pubic bone. The main function of the ligaments is to keep the penis and the scrotum properly positioned.
The suspensory ligament is attached at the base, and surrounds the CC. The best way to stretch the suspensory ligament is to stretch straight down. The fundiform ligament is also located at the base of the penis. It surrounds the shaft and continues into the scrotum, supporting both structures. By stretching your penis to the side, you should feel a slight pull in your fundiform ligament.