Rat reproductive system
NOTE: You are dissecting only one rat; therefore, you will only see one sex during the actual dissection. You are, however, responsible for knowing the reproductive organs of both the male and female. Be sure to prepare your specimen so that it will be clear enough for another student to study. Also, make certain you examine a specimen of the sex that you did not dissect.


Locate the scrotum, a large sac of skin, muscle and connective tissue containing the testes on the exterior of the body just ventral to the anus. During non-breeding periods, the testes may be retracted into the abdominal cavity and the scrotum will not be enlarged. However, sperm cannot develop completely within the high temperatures of the abdominal cavity; the slightly lower temperature of the scrotum is necessary for the final stages of sperm formation.
Carefully cut open the scrotum and locate the paired testes, which are oval. Around the outside of each testis is a C-shaped structure known as the epididymis, which is a very long, highly coiled tubule. Three regions of the epididymis can be recognized: the caput (head) epididymis covering the anterior end of the testes, the corpus epididymis lying along the lateral surface of the testes and the cauda (tail) epididymis on the posterior end of the testes. Sperm cells produced in the seminiferous tubules of the testes pass into the caput epididymis via the vas efferentia (very small tubules that are not visible). Then, the sperm cells move through the corpus and cauda epididymis into the vas deferens, which is a moderately large tube leading from the epididymis to the urethra which is a tube located inside penis. Notice that the penis is enclosed in an epithelial sheath and held along the ventral wall of the abdomen (Figure 10, 12).
The prostate glands are found on either side of the urinary bladder. Locate the large, lobed vesicular glands, and the coagulating glands, which are closely applied to the inner curve of the vesicular glands. The above glands and some other glands in this region comprise the accessory sex glands. The secretions of these glands form the seminal fluid, which carries the sperm during ejaculation, activates and provides certain nutrients for them, and contains substances, which neutralize the somewhat acid environment in the vagina.
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Figure 12: Pictures of the male rat reproductive system.
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Locate the ovaries, which appear as a mass of follicles just posterior to the kidneys. They are often buried in a mass of fat, which should be carefully removed. The adult non-pregnant rat is usually in breeding condition with mature or well-developed ova in the ovaries. The oviducts are small highly coiled tubes leading from the ovaries to the uterus. Locate the right and left cornua (horns) of the uterus. The cornua of the uterus unite to form the vagina (Figure 9, 13).
Open one horn of the uterus and examine the interior for embryos, which might be present. The vagina leads to the exterior separately from the urethra. The vagina opens to the exterior via the external vaginal orifice, which opens just posterior to the urethral opening. The clitoris, which is the female homolog of the male penis, is associated with the urethra and therefore is not connected with the vagina in the rat.
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Figure 13: Pictures of the female rat reproductive system.
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