Morphology
Mouse (Mus musculus)
The mouse is lhe most Iamiliar and widely dislrib- I tiled rodent in lhe world. The house mouse is about 6-X cm in length, excluding ils long Iiiil which is usually the same length as lhe body, and weighs about 20-40 g.
Il hi∣s a small Iieiid with a pointed nose and a split upper lip. Arnmged around lhe area of the upper lips are several long thin whiskers which help the mouse Io find its way around in lhe di∣rk. The ears arc very delicate, short and rounded. The eyes are large, dark and protuberant and provide a wide range of monocular vision. Their sight is poorlv developed and they are pholαphobic. The long prehensile tail is almost Iiiiirless and covered in visible scales. Mice hi∣vc four toes on the front feel and live on lhe Iiindfecl: each Uκ∙ ends in a small claw. Female mice Iuive seven pairs of teats but they arc absent in the male.The Iiaturiil colour of the mouse is greyish brown with a lighter underside. However, as a result of selective breeding, pct mice, known as fancy mice, can lx∙ found in a wide range of coal lengths and textures, colours, colour Conibinalions. and with red or black eves.
Rot (Rattus norvegicus)
Γhc genus Riiltus conti∣ins about XO species of rat but it is the brown nil lluιt Iuis been developed into the ∣x∙t or Iitboriilory nil. They weigh from 400-X00 g. adult Iiiiilcs being much larger lluιn lhe females. The body shape ol the rat Issimiliirtothaloflhemousebul nils i∣re Considenibly larger. The prehensile tail is thick and rasp-like and covered in scales. As in mice, nits have four Iocs on lhe forefeet and live on the Iiindfccl. each ending in a small claw. Femalc rats have live pairs of Ieals but Ihcy are absent in males.
Raltns Iiorvnjicus is Iiiitunilly brown but selective breeding hits produced Iancv nils with a wide range of coat colours, patterns and eye colours.
It is unnecessary to starve small rodents prior to anaesthesia - the stomach is impossible to empty as it usually contains ingested faecal pellets. Regurgitation and choking is unlikely to be a significant risk. Rodents have a high metabolic rate so starvation may result in a fatal hypoglycaemia.
∕∖ll the myomorphs show varying degree of Coprophagia. i.e. eating their own faeces. The faecal pellets may contribute a significant proportion of nutrients to the diet and are rich in vitamin B. produced by microorganisms living in the colon.