SUB-FAMILY MURINAE. 



Incisors compressed laterally. Molars Izl or !_?, 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 abore 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 Is. 



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 : 



MURES. Old World Rats. Molars very large and broad. Those in the upper jaw with three 

 tubercles in each transverse series. 



SIGMODONTES. 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 



