INTEGUMENT
The hair is divided into guard hairs and undercoat. The wild color is agouti, meaning brown and black on top with a lighter underbelly. The rat has tactile vibrissae which are essential for the animal's orientation.
They have sensory bulbs at their base, and an extensive nerve and blood supply. There are 50 to 60 of them located on each side of the upper lip and nose in 8 to 10 rows and they are innervated by the infraorbital nerve. Smaller tactile hairs are also found on the lower lip, chin, and upper eyelid (Hebel & Stromberg 1986e).Older entire male rats often develop yellow-brown sebaceous secretions along the dorsum, which are often confused with mites or lice. This effect is enhanced by testosterone and inhibited by estrogen (Fallon 1996).
KEY POINTS
• Open rooted, yellow incisors; closed rooted molars
• Lower incisors are 2 to 3 times longer than upper
• Stomach has glandular and non-glandular portions
• No gall bladder
• Female has a duplex uterus and urethral orifice is separate from vulva
• Extensive mammary tissue from axilla to groin in female
• Acute sense of smell and hearing
• Prominent Harderian gland which hypersecretes “red tears”