ZOOLOGICAL GARDENS. 
21 
siderable diversity of structure, as in some they have 
roots, while in others they are always growing. Milk 
teeth, which occur in the majority of other animals, have 
not been detected in a large number of rodents, and 
when they do exist, as in the Guinea-pig, they are shed 
before the animal is born. 
Some of these animals, like the Old World Monkeys, 
have huge sacs at the angles of the lower jaw called buccal 
pouches, and, in the Hamster, they can be drawn back 
by special muscles, which are attached to processes of the 
back-bone in the loins of the animal. Many of them 
are burrowers and nocturnal in their habits. A few of their 
structural modifications are exhibited in this house; 
and a little to the south-east, the animals known as 
porcupines, have a special house devoted to themselves. 
In this Rodent House, the forms exhibited are, the Paca 
or Spotted Cavy, the Agouti, the Viscacha, the Coypu, the 
Guinea Pig, the Hare, the Hispid Hare, the Bamboo Rat 
the Indian Field Rat, the Marmot, and Squirrel, the last 
being illustrated by a number of species, some being 
accommodated in other parts of the Garden. 
The Spotted Cavy is an inhabitant of South America, 
and along with the Agoutis, constitutes a Family of Rodents. 
Its greatest peculiarity is the very remarkable cavity that 
occurs in the cheek and lies under a great expansion of 
what is called the zygomatic arch, that is, the eminence 
corresponding to the line that runs from the ear of man 
to the bony prominence of his cheek. A dilatation 
of this character is not found in any other animal. The 
sac that lines this great bony cavity, is an inward prolong¬ 
ation of the skin of the cheek, devoid of hair, and the open¬ 
ing being placed behind the mouth might at first sight be 
