A LABORATORY MANUAL OF 

 THE ANATOMY OF THE RAT 



INTRODUCTION 



The rat is one of the few wild mammals that thrives in 

 civilized communities. It reproduces rapidly, consumes or 

 otherwise destroys millions of dollars worth of property, 

 and is the known, or probable, carrier of several parasites 

 harmful to man. Some of these parasites are : Leptospira 

 ioterohaemorrhagiaey the spirochaete organism of infectious 

 jaundice ; germs which cause diseases in man following rat 

 bites, for instance rat-bite fever; the tapeworm Hymeno- 

 lepis diminuta, and possibly its relative H. na/na; the 

 round worm, Trichinella spirwlm, which causes trichiniasis ; 

 and Bacillus pestis, the germ of plague. It is claimed that 

 the plague, or ''black death," killed 25,000,000 people in 

 Europe during the fourteenth century, and that plague has 

 caused the death of nearly 9,000,000 persons in India alone 

 since 1896. The rapidity and ease with which rats can be 

 bred has led to their extensive use in experiments by physi- 

 ologists, geneticists, and others. It is evident, then, that an 

 elementary knowledge of the habits, functions, and struc- 

 tures of the rat is of interest to the medical student, 

 anatomist, agriculturist, and experimental zoologist. 



The rat belongs to the order ^Bodentia, which includes 

 over one-third of all existing species of mammals. Rodents 

 possess long, chisel-like, curved incisor teeth (usually but 

 two in the upper jaw, and never more than two in the 

 lower) , which grow continuously. The enamel is restricted 



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