INTRODUCTION
GENERAL EXTERNAL ANATOMY
The name guinea pig has become synonymous with the term “experimental subject” in medical research. This is because the guinea pig was the first animal to be used in research: in an experiment on heat production in 1780 (Wagner 1976).
The wild ancestor of the guinea pig, Cavia porcellus, comes from South America where they lived in small groups in grassland areas (Harkness & Wagner 1995). Cavia porcellus no longer exists in the wild and was domesticated for centuries by the Incas for religious and food purposes (Nowak 1999). The early conquistadors invading Peru from 1532 called them Indian pigs because, at the time, South America was thought to be part of the West Indies and their squeals resembled that of pigs. The origin of the word “guinea” is lost in history. Theories range from claims that they cost one guinea when first imported as pets to 16th-century England or that they came via the Dutch colony of Guyana and the name later became corrupted (Wagner 1976; Weir 1974).
The word cavy is the correct term as it derives from the South American Quechuan (vernacular). Although that is also the scientific name, the name guinea pig is still more commonly used today.
Although the guinea pig has much in common with rats and mice from a morphological perspective, recent genetic research has indicated that the caviomorphs may have evolved separately. Examination of mitochondrial DNA has shown that they may be more closely related to man, rabbits, horses, seals, and cows than to rats and mice (D'Erchia et al. 1996; Harkness & Wagner 1995).