632 MURID^— MUS 



distribution in southern Asia and in Africa, and having no near 

 relationship with any other genus, except the Indian Legga- 

 dilla, which may be regarded as an offshoot. The genus 

 betrays a high degree of specialisation, and as regards its 

 dental characters it undoubtedly stands on a loftier plane than 

 does any of the other members of the sub-family dealt with in 

 this work. 



Externally this genus does not differ noticeably from 

 Epimys, but all the known species of Mus are of small size. 

 The females have ten mammae, arranged in three pectoral and 

 two inguinal pairs. 



In the skull the brain-case is rather small and depressed ; 

 there are no interorbital beads (present in Leggadilla), and 

 the temporal ridges of the brain-case are very feebly developed ; 

 the zygomatic arches are relatively strong, particularly as 

 regards their anterior maxillary portions, and there is a small 

 peg-like process on the outer side of each maxilla below and 

 just in front of the lower zygomatic root, which serves for the 

 attachment of the tendon of the anterior part of the masseter 

 lateralis muscle. 



In the dentition the upper incisors are strongly curved, 

 terminating behind in the maxilla between m^ and the maxillo- 

 premaxillary suture. The disc of wear is peculiar, there being 

 a well-marked notch on the outer side just behind the junction 

 of the white dentine with the yellow enamel. Winge explains 

 this feature by supposing the dentine to be harder at the 

 postero-external corner of the tooth than elsewhere ; Miller, on 

 the other hand, attributes it to the angle at which the teeth 

 are set. We are not able to find any appreciable difference 

 between Mus and Epimys as regards the " set " of the incisors, 

 and would attribute the notch rather to the increased strength 

 and peculiar mode of action of the ntasseteres laterales muscles, 

 which have induced several much greater modifications in the 

 structure of the cheek-teeth as well as in the skull itself. 



The lower incisors terminate behind, near the bases of the 

 condylar processes, their ends producing rather well-marked 

 humps on the outer surfaces of the mandible. 



Cheek-teeth (PI. XXVIII., Fig. lo):— In this genus m\ 

 are relatively large, being as long as or longer than »4^ 



