THE BROWN OR COMMON RAT 619 
16-4 to 22; diastema, 12 to 15-6; maxillary tooth-row, 6-8 to 8-8; 
mandible, 26 to 33; mandibular tooth-row, 6-8 to 8-4. 
Distinguishing characters :—The Common Rat in all colour phases 
is readily distinguishable from any sub-species of 4. rattus by its 
stouter build, greater weight (in relation to length of head and body), 
shorter tail, shorter and thicker ears, and its larger hind feet. The 
skull is characterised by its greater size and the peculiarities of form 
in the parietal and interparietal regions described above. 
The Common or Brown Rat is probably the most injurious 
and universal mammalian pest of the human race, and its 
habits are so well known as not to require description; or, 
rather, they are so wide as to be comparable with those of man 
himself, and would therefore require a volume for exhaustive 
treatment. It does not appear to have a single redeeming 
feature, its value as a scavenger being now negligible. 
Disregarding exceptional conditions, rats are wide-foraging 
animals, dwelling in secure burrows,’ where they lie up in a 
warm nest of grass or other materials, and to which they carry 
their food, at least when abroad by daylight; but probably 
from reasons of prudence their forays take place chiefly at 
night. Being powerful diggers, they are quick to construct 
new burrows in the neighbourhood of food, and sometimes 
these are merely temporary shelters, not occupied for purposes of 
sleeping. The proximity of the food supply usually governs the 
situation of the burrow, but there is no rule for its extent or 
situation ; it generally consists of several winding galleries, and 
possesses more than oneentrance. The animals are apparently 
loth to make unnecessary excavations, and they are quick to 
burrow in heaps of soft material, such as manure (which is 
also warm). For the same reason, perhaps, they are great 
frequenters of ricks,? which also supply them with food ; of the 
burrows of rabbits, where they devour the young; and above 
all of dwellings and outhouses, where they lie up in the floors, 
walls, or more rarely, in the roofs (though common in thatch). 
Their teeth are so powerful that they rapidly gnaw a way 
through wooden partitions; they have been known to damage 
1 Sometimes at a distance from their food—see Fie/d, 17th July 1886. 
2 Owen Jones records the capture of 600 rats from one rick, 1000 from two, and 
1300 from three other ricks. 
