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A tail vein is a structure that carries blood back from the tail to the heart in a vertebrate. The vein leads to the posterior cardinal vein in the backside of an animal, a common feature of rodent anatomy. Muscular and skeletal structures decrease in size toward the tip of a tail, but veins remain the same diameter throughout the length of it. This makes any vein more prominent toward the distal part of a tail, and easily accessible. The walls of a tail vein are elastic and can stretch, making the tail a good location for scientists to draw blood from mice or rats.
Blood from a mouse is usually drawn from the lateral tail vein. The primary puncture site is one-third down the length of the tail from the tip. If more samples are needed, these can be taken at other sites moving toward the base. Like in human blood vessels, pressure can be used to stop bleeding after a needle is removed.
Rat tails have two lateral veins, one on the right side and one on the left, and a dorsal vein in the mid-section, which become more prominent when compared to the general anatomy toward the tip. There is just one vein, up to 0.15 mm (about 0.006 inches) in diameter, in the end segment of a rat tail. On the segment closest to the body, a vein is found on each side near the tail’s midline.
The tail vein can often be reached without sedating an animal. Warm water is usually enough to dilate blood vessels, and laboratory subjects can be returned to their spaces after the procedure is completed. Veins in the tail are also located under the skin, so are easier to reach than the corresponding artery, which is located beneath other tissues as well.
A dorsal coccygeal vein is another tail blood vessel that can be found in rodent and animal anatomy. All of these veins make up a general pattern seen in tail anatomy. Variations in the position of blood vessels should be taken into account if initial samples aren’t successful. Veterinary specialists that treat household pets and horses are well-versed in tail anatomy. It is also widely studied by laboratory researchers who work with mice and rats and need to take regular samples to obtain study data.