502 HARES AND RABBITS CHAP. XV 
though truncate at the free extremity and hollow; they represent 
in a more rudimentary way the much stronger tuft at the end of 
the tail of other Porcupines. It is a curious fact that this and 
other Porcupines possess a mechanism for warning their foes 
precisely comparable to that of the rattlesnake. There are 
sixteen dorsal vertebrae. 
SuB-ORDER 2. DUPLICIDENTATA. 
The chief feature of this group is the existence of two pairs 
of incisor teeth in the upper jaw, of which the inner are very 
small and le behind the outer. In the skull the infra-orbital 
foramen is small; the incisive foramina are very large. The tail 
is short or absent. 
Fam. 1. Leporidae.—This family is distinguished from the 
Lagomyidae by the long ears, by the tail, which is present, though 
short, and by the longer limbs. There are six teeth belonging to 
the molar series in the upper jaw, and five of the same in the 
lower. The clavicle is imperfect. 
The longest known genus of this family, Zepus, was, until the 
quite recent discovery of Romerolagus, the only genus. It is of 
universal range, excepting Australasia and Madagascar, and con- 
sists of about sixty species. These are the Hares and Rabbits, to 
the former being assigned the longer-lmbed forms. 
As every text-book of zoology contains a more or less elaborate 
account of the structure of the Common Rabbit, and as there is 
but little structural difference between the members of the genus, 
a short account of the generic peculiarities of ZLepus will suffice 
here. The fore-feet are five-toed, the hind-limbs four-toed. The 
hairy integument enters the mouth cavity, and the inside of the 
cheeks have a hairy covering. The soles of the feet are, more- 
over, hairy. The maxillary bones are curiously sculptured. 
The Common Rabbit, Z. cunieculus, differs from the Common 
Hare in the comparatively shorter ears and legs. The ears have 
not, to so marked a degree, the black tips of those of the Hare. 
The animal, moreover, produces naked young, and lives in burrows 
of its own excavation. A difference in the structure of the 
caecum, which distinguishes the Rabbit from the Hare, has been 
