Corpus spongiosum is the correct answer.

The penis is composed of several structures, including the corpora cavernosa and the corpus spongiosum. These structures are made up of bundles of muscles, connective tissue, and blood vessels.

Corpus cavernosum:
- The corpus cavernosum is one of the two cylindrical masses of erectile tissue that run along the length of the penis.
- It is composed of numerous bundles of smooth muscle fibers and connective tissue.
- The muscle fibers in the corpus cavernosum are arranged in a mesh-like pattern, allowing it to expand and contract during sexual arousal and ejaculation.
- When the penis is flaccid, the muscle fibers are relaxed, allowing blood to flow freely through the tissue. During an erection, the muscle fibers contract, trapping blood within the tissue and causing the penis to become erect.

Corpus spongiosum:
- The corpus spongiosum is another cylindrical mass of erectile tissue that surrounds the urethra, which is the tube that carries urine and semen.
- Unlike the corpus cavernosum, the corpus spongiosum contains fewer bundles of smooth muscle fibers.
- It is made up of a spongy network of connective tissue and blood vessels.
- The main function of the corpus spongiosum is to keep the urethra open during erection, allowing for the passage of urine and semen.

Difference between corpus cavernosum and corpus spongiosum:
- The corpus cavernosum is located on either side of the penis, while the corpus spongiosum is located in the midline.
- The corpus cavernosum contains more bundles of smooth muscle fibers compared to the corpus spongiosum.
- The corpus cavernosum is primarily responsible for the rigidity of the penis during an erection, while the corpus spongiosum helps keep the urethra open.

In conclusion, the corpus spongiosum is the bundle of muscles in the penis area, while the corpus cavernosum is composed of smooth muscle fibers and connective tissue.