Fox urogenital system
Photos and Text: Nick Zolkowsi and Elizabeth Farrell
Although functionally distinct, the urinary and reproductive systems are commonly considered together, and referred to as the urogenital tract. In males, sperm and urine exit the body through the same structure. While there is a similar transient connection between the two systems early in the female embryo, it is lost as development proceeds. [1]
The urinary system consists of two kidneys, two ureters, a bladder, and a urethra. The kidneys function to filter waste from the bloodstream, producing urine, which passes from the kidneys through the ureters to be stored in the bladder. Urine then leaves the bladder and exits the body through the urethra. It is at this point that, in males, there is a connection between the urinary and reproductive systems, as the urethra serves as a passageway not only for urine, but for sperm as well.
The reproductive system in the female consists of the ovaries, uterus, fallopian tubes, and vagina. Across Mammalia, the size and shape of the uterus is highly varied, with the fox uterus having two uterine horns. In males, the system is comprised of the scrotum, testes, ductus deferens, epididymus, urethra, and penis. Both males and females have erectile tissue associated with the reproductive tract. Fertilization takes place when sperm released from the penis via the ejaculatory duct enters the vagina and travels up the reproductive tract, where it will penetrate an egg. The fertilized egg then implants in the uterus, where development will occur. The length of pregnancy varies considerably across Mammalia, averaging eight weeks in the fox. The number of young per birth is also highly variable, with a typical fox litter containing three to four young [2].
Our specimen was female, and as it appeared full grown, could be assumed to be of reproductive age. Female foxes reach sexual maturity at ten months old [2]. However, given the small size of the uterus, it is unlikely that it had ever been pregnant.
Both the urogenital system and the digestive system have connections to the inferior vena cava, and as a result, when we removed the digestive tract, we accidentally took the urogenital system with it. To avoid this, before beginning either dissection, it is important to locate the organs which you intend to remove, and also those which are in close proximity. A preliminary separation of the two systems should prevent a similar mistake from occurring in the future.
The furthest cranial structures in the urinary tract, the kidneys lie dorsal to the stomach and digestive system, with the right kidney slightly more cranial than the left. Each kidney is 8 centimeters long and about 4 centimeters in diameter. There are no distinguishable differences between the two. Each is surrounded by fatty mesentery tissue that was removed. Judging from the amount of fat present, our fox was likely well fed. We cut the right kidney along its frontal border to see a cross-section of it. We observed the medulla, the cortex, and the renal pelvis. The medulla was a slightly darker color than the cortex, but the two were not greatly differentiated. Arising from the renal pelvis of the kidneys are the ureters, which lead to the bladder. These ureters greatly resemble nerves in physical appearance. The bladder lies at the midline of the body, cranial to the pubic bone. Our specimen's bladder was quite small, with thick walls that would expand in a living animal to store urine. We were also able to see and palpate the urethra, which leaves the bladder caudally and opens into the vagina to excrete urine.
In the reproductive tract, the uterus is the furthest caudal structure. In the fox, the uterus splits into two uterine horns, right and left, at its cranial end. These horns lead to the right and left ovaries, respectively. The horns are not straight, but bundled amongst a mass of mesentery, which was cut and removed so as to untangle the horns. We located the ovaries at the end of the horns. The ovaries are small, and difficult to differentiate from mesentery. At the caudal end of the uterus is the cervix, which leads into the vagina dorsal to the urethra and ventral to the anus.
1. Cartmill, M. et al. Human Structure. Harvard University Press. Cambridge, MA. 1987.
2. Alderton, David. 1994. Foxes, Wolves, and Wild Dogs of the World. Facts on
File, New York.
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