24 
CENTRAL HALL. 
characteristic of different groups ; wliile below are a few of the 
different types of tails. Very instructive is a series of skins of 
white chickens of the same brood at different ages displaying 
the gradual replacement of the down by the adult plumage. 
The table-case in the middle of the bay contains illustra- 
tions of the external characters, the beak, the feathers, and the 
tail, as well as of the fore and hind limbs, or wings and feet. 
By the aid of the explanatory labels, the essential characters 
and the principal modifications of all these parts can easily 
be followed. 
Bay IV. The fourth bay on the west side of the hall exliibits the 
tme^of leading peculiarities in the structure of Eeptiles and Amphi- 
Reptiles and bians. Owing to the large number of groups in the former 
Amplnbians. (.^g^gg ^hich are now extinct, many fossil specimens, or plaster 
reproductions of the same, are shown. The wall-case on the 
south side of this bay illustrates the different ordinal groups of 
reptiles — living and extinct. Yery instructive are the skeletons 
of Tortoises and Turtles, showing the relations of the vertebrae 
and limb-bones to the bony shell. Lizards and Snakes are 
mostly represented by coloured casts. The extinct Dinosaurs 
are represented by a small-sized model of the Iguanodon, 
together with a photograph of the skeleton and a plaster-cast 
of the bones of the hind-foot showing the three toes. 
The adjacent side of the table-case shows the modifications 
of the backbone, or vertebral column, of the ribs, and of the 
limbs, in the different groups of the class. Specially noticeable 
are examples of five types of Skink-like Lizards, exhibiting the 
gradual diminution in the size of the limbs and their final 
disappearance. 
The opposite, or north, side of the table-case displays the 
different modifications' in the skull and teeth of living and 
extinct Reptiles. In some, like Crocodiles and Jchthyosaurs,. 
the jaws are armed with a full series of sharply pointed teeth,, 
while in others, like the Tortoises and Turtles, they are devoid 
of teeth and encased in horn. Very remarkable is the 
approximation to a carnivorous mammalian type presented by 
the dentition of some of the extinct Theromorphs, and equally 
iioticealde are the palatal crushing teeth of certain other members 
nf the siimc group (Placodits and Cyamodiis). The peculiar den- 
