Sus-Famity MURINAE. 
Incisors compressed laterally. Molars $-* or —s rooted, the anterior largest, the posterior smallest. Ante-orbital 
foramen a deep narrow slit, widening above. Palate mostly on one plane. Descending ramus of lower jaw with the 
angles not situated above the plane of the crowns of the molars. 
The above characters furnish some of the most striking peculiarities of the skull by which 
the Murinae differ from Arvocolinae. Others will be found detailed at length in the descrip- 
tions of the different genera. In many points the two sub-families are very closely related, so 
much so, indeed, as to render it somewhat unnatural to separate them. Still, as this can be 
done by well-marked characters, it is, perhaps, best to do so, especially in view of the very 
large number of species. 
In further illustration of the peculiarities of the Murinae it may be stated that the glenoid 
cavity is considerably elongated and moderately wide. The posterior margin of the palate is 
usually behind the line of the posterior molars. The incisive foramina are large, and situated 
partly in the intermaxillary, partly in the maxillary bones. There are two moderately large 
foramina in the palato-maxillary suture. The coronoid process of the lower jaw is usually 
large, and the condyloid elongated. The descending ramus approaches more or less a quadrate 
form. The posterior lower angle is rounded, and the upper angle is acute. 
The molars of the Murinae have transverse ridges on the unworn crowns, each ridge usually 
broken up into a series of tubercles. There are usually three such ridges on the first or anterior 
molar, two on the next, and on the last, one and a half. As the crowns wear away the tubercles 
disappear, until there is visible only the border of enamel, with undulations or transverse fol 1s. 
The feet of the Murinae are usually naked beneath ; even when the heel is hairy the toes are 
naked and transversely ridged ; the number of tubercles on the soles varies somewhat. The 
tail is more or less scaly, the scales arranged in whorls, with hairs passing out between the 
whorls, sometimes in such number or length as to conceal the scales entirely ; these are, how- 
ever, most generally visible. 
The characters of the Murinae, as given above, although derived chiefly from the typical 
forms, apply pretty well to all the species throughout the world. There are, however, important 
differences, which serve to separate the Old World species from the New, and render expedient a 
further division into Mures and Sigmodontes—the former confined entirely to the Old World, the 
latter found only in America—and neither occurring wild with the other, except through human 
agency. It thus becomes possible, in all cases, to decide at once whether a given species caught 
on this continent is really native or has been introduced. They may be characterized briefly as 
follows : z 
Movres.—Old World Rats. Molars very large and broad. Those in the upper jaw with three 
tubercles in each transverse series. 
Sremopontes.—New World Rats. Molars narrower. Those of the upper jaw with two 
tubercles or points in each transverse (or slightly oblique) series. 
There are other differences, which will hereafter be referred to. It will be sufficient to add, 
that the possession of the larger teeth seems to impart to the Old World rats a greater degree 
of ferocity and strength, rendering them more cosmopolite and omnivorous than the American 
