zoo MAMMALIA ORDER V.RODENTIA. 



molars having flat crowns, with complicated foldings of enamel, and the 

 somewhat bushy tail being cylindrical. The more northern repre- 

 sentatives of the family take their name from the long winter torpor they 

 undergo. 



From the Myoxidce, the very extensive and cosmopolitan family of the 

 Muridce, which includes rats, mice, and voles, may be distinguished by the 



total absence of premolar teeth in both jaws. The group is, 



The Mouse Tribe, however, better characterised by the structure of the skull, 



Family Muri- in which the frontal bones are markedly constricted, while 



dee. in the zygomatic arch the short and slender jugal bone is in 



most cases reduced to a small splint connecting a back- 

 wardly-directed process from the upper jaw-bone, or maxilla, with a forward 

 projection from the Bquamosal bone at the hinder end of the skull. Still 

 more characteristic is the expansion of the lower part of the first-named pro- 

 cess into a large, flattened descending plate ; and in most cases the large 

 aperture in the skull for the passage of nerves situated beneath the anterior 

 root of the zygomatic arch is elevated, and much wider above than below. 

 The first toe of the fore-foot is rudimental, and in most cases naked and 

 scaly. This family, which includes more than a third of the members of the 

 entire order, is the only one among the Rodents represented either in 

 Madagascar or in Australia. Although a few species are aquatic, and some 

 arboreal, the great majority of the Muridce are terrestrial, a considerable 

 number of them living in burrows. Some fifty genera have been described. 



The first sub-family is confined to Australia, New Guinea, and the island 

 of Luzon, in the Philippines, where it is represented by three genera. In 



this group the molars, which are frequently reduced to two 



The Australasian pairs in each jaw, develop roots, and have their crowns 



Group. divided into alternating oblique lobes, partially splitting up 



Sub-Family into tubercles. In the typical genus Hydromya, of Australia 



HydromyincE* and New Guinea, the molars are J:wo in number, and the 



external form is modified for the needs of an aquatic exist- 

 ence, the feet being webbed, the tip of the muzzle thickly clothed with hairs, 

 by means of which the nostrils can be clothed ; while the skull differs from 

 that of other members of the family in that the aperture beneath the socket 

 of the eye is nearly circular, instead of pear-shaped, and the descending 

 vertical plate at the front of the zygomatic arch is absent. In habits the two 

 species of this genus resemble water-voles. The genus Chrotomys, of which 

 there is one species from Luzon, differs from the other two in having three 

 pairs of molars ; its skull being intermediate between that of the first and 

 third genus, and its external form mouse-like, the toes being devoid of webs, 

 In JTeromi/s, which occurs typically in Australia, but is taken to include a rat 

 from Luzon, the molars resemble those of Hydromys in structure and number, 

 l;ut the skull and external form are nearly similar to those of an ordinary 

 mouse. _ In size this species is not larger than the common mouse, whereas 

 the other members of the group are much bigger. 



The second sub-family is represented only by the beautiful little Malabar 



spiny mouse (Platacanthomys lasiurus) of Southern India, 

 Malabar Spiny which is an arboreal form easily distinguished by the long 

 Mouse (Plata- bushy tail, which exceeds the head and body in length, and 

 canthomyince). also by the presence of flattened spines mingled with the 



hairs. The rooted molars have their crowns divided into 



complete transverse laminse. 



