Mice, like most mammals, possess a distinct and complex reproductive anatomy, and male mice do have a penis. This organ is an integral part of the male reproductive system, facilitating the transfer of genetic material necessary for procreation. The structure of the mouse penis shares general mammalian characteristics but is uniquely adapted to its reproductive strategy, including the formation of a physical barrier after mating.
Anatomy of the Male Mouse Reproductive System
The mouse penis is located on the ventral side of the body, positioned anteriorly to the anus. The external portion is typically retracted and consists of the prepuce and the glans penis. The glans region contains specialized structures instrumental during copulation.
A unique feature of the male mouse’s anatomy is the presence of the baculum, or os penis, a small bone found within the penile tissue. This bone provides rigidity to the organ, which is necessary for mechanical stimulation of the female reproductive tract during mating. The width of the baculum shaft has been shown to correlate with a male’s reproductive success when competing with other males.
The internal reproductive tract includes accessory glands, such as the seminal vesicles and coagulating glands, which produce the fluid components of the ejaculate. These secretions mix with sperm during ejaculation to form a coagulated substance. The components are ultimately delivered through the urethra, which runs the length of the penis.
How to Visually Determine the Sex of a Mouse
The most reliable method for visually distinguishing a male mouse from a female, especially in newborns, is by examining the Anogenital Distance (AGD). The AGD is the measurement between the center of the anus and the center of the genital papilla, the external genital opening.
In male mice, the AGD is significantly longer, measuring approximately twice the distance found in females. This difference results from the influence of androgens, or male hormones, during fetal development. The greater separation between the two openings is a clear indicator of the male sex, often visible from birth.
Secondary indicators can also assist in sex determination, particularly in older mice. The female’s genital papilla is closer to the anus and appears more circular, while the male’s genital opening is further away and often more pointed. Additionally, adult females possess visible nipples, which are not present in males.
Function and Development of Mouse Sexual Organs
The primary function of the male mouse’s sexual organs is the delivery of sperm into the female reproductive tract for fertilization. During copulation, the male deposits an ejaculate that rapidly coagulates to form the copulatory plug. This plug is a dense, temporary barrier that seals the female’s vaginal opening.
The copulatory plug serves several purposes, including preventing the leakage of ejaculate and ensuring effective sperm transport within the female. It also functions competitively by delaying the female from mating with rival males immediately afterward. Research suggests the plug can also influence the female’s reproductive physiology, potentially promoting successful implantation of embryos.
The development of the male reproductive system begins early in gestation, with sexual differentiation starting around 16 days. Male organs develop from an ambisexual genital structure under the influence of prenatal androgen hormones. This hormonal exposure dictates the final male phenotype, including the elongated anogenital distance and the formation of the distinct external genitalia.