1290 



THE RODENTS 



cases there is no great disproportion between the length of the fore and hind-limbs. 

 The incisor teeth are narrow, and, owing to the invariable absence of premolars, 

 there are never more than three pairs of cheek-teeth in each jaw. 



In structure these teeth exhibit great variation in the different groups, being 

 either furnished with roots, or rootless, while in some cases their crowns are sur- 

 mounted with simple cusps, and in others with folds of enamel arranged in a series 

 of angles. In all cases the first toe of the fore-foot is rudimental. The skull is the 

 most characteristic part of their entire organization, although it is difficult in a pop- 

 ular work like the present to point out its distinctive peculiarities without the aid of 

 a series of figures. It may be mentioned, however, that the frontal region between 

 the eye sockets is much narrowed, and that in the zygomatic, or cheek arch, the 



cheek (jugal) bone is 

 usually reduced to a 

 mere splint occupying 

 the middle of the arch. 

 Again, the lower sur- 

 face of the process 

 arising from the upper 

 jawbone to form the 

 front half of the 

 cheek arch is more or 

 less flattened out into 

 a nearly perpendicular 

 plate; while the vacu- 

 ity in the front of the eye for the passage of the nerves of the face is generally of 

 considerable height and wider above than below. 



The number of genera and species belonging to this family is so great that it 

 is impossible to notice more than a small moiety in this work. Accordingly, only 

 representatives of the various subfamilies into which these Rodents are divided, and 

 such forms are of general interest, are selected for description. 



SKELETON AND MOLARS OF BROWN RAT. 



THE AUSTRALIAN RATS 



The Australian rats, of which there is one aquatic species, together with an 

 allied terrestrial form from the same region, constitute a subfamily distinguished 

 from all the other mice by having only two pairs of molar teeth in each jaw; these 

 teeth being rooted, and having their crowns divided into distinct lobes. 



The Australian water rat (Hydromys chrysogaster] is a rat-like aquatic Rodent, 

 with broad and partially-webbed feet, the webs and claws being larger in the hinder 

 than in the front-limbs. The fur of the back is black with an admixture of golden- 

 colored hair; the under parts being of a dark golden hue, save for a narrow stripe 

 of flaxen running from the lower part of the neck to the middle of the belly. Ex- 



