INTRODUCTOEY COLLECTION. 
25 
The central case of the bay contains a collection illustrat- Teeth of 
ing the principal characters of the teeth in the Mammalia. 
Its inspection should commence at the north-east corner, where 
the visitor will find himself, after completing the survey of the 
osteological specimens in the wall-cases. In the first division 
specimens are placed showing the general characters of 
teeth, their form, the different tissues of which they are 
composed, the two great types of dentition in mammals, 
homodont and heterodont, the nomenclature and homologies of the 
different teeth, and their development and succession. The 
principal modifications of teeth according to their function are 
next shown, by examples of forms adapted for fish-eating, flesh- 
bating, insect-eating, grass-eating, &c. The remainder of the 
case is taken up by select examples of the dentition of all the 
different families of mammals arranged in systematic order, 
prepared so as to display not only the shape of the crowns, but 
^llso the number and character of the roots by which they are 
implanted. 
Bay No. II. contains, in its first wall-case (the only one yet Bay II. 
occupied), illustrations of the outer covering or integument and Jf ^I^Sls 
its modifications in the class of Mammals, divided into the 
following sections : 
1. Expansion of skin to aid in locomotion, as the webs 
between the fingers of swimming and flying animals, the para- 
chutes of flying animals. 
2. The development of true bony plates in the skin, found 
among mammals only in the Armadillos and their allies. The 
cast of a section of the tail of a great extinct species {G-lyptodon) 
shows well a bony external as well as internal skeleton. 
3. The outer covering modified into true scales, much resem- 
bling in structure the nails of the human hand. This occurs 
in only one family of mammals, the Pangolins or Maiiidce. 
4. Hair in various forms, including bristles and spines. A 
stuffed specimen of a Porcupine at the bottom of the case 
affords a good illustration of a spiny covering. The two 
kinds of hair composing the external clothing of most mam- 
mals, the long, stiffer outer hair, and the short, soft under 
fur, are shown by various examples. 
5. The special epidermal appendages found in nearly all 
