STRUCTURE OF BIRDS. 
19 
8. The antlers of Deer, solid, bony, generally branched, projec- 
tions, covered during growth with soft vascular hairy skin, and 
in most cases shed and renewed annually. 
Against the wall at the back of the bay is a case containing 
a series showing the changes in the dentition of the Horse at 
different ages. Above this is arranged a series of antlers of the 
Stag or Eed Deer {Cervus elaphus), grown and (except the last) 
shed in thirteen successive years, showing the changes which 
took place in their size and form, and the development of the 
branches, or tines, in each year. In old age the number of 
these tines tend to diminish. 
The other systems of organs of the class will occupy the 
north side of the central case of this bay. 
Bay No. III. is devoted to the class of Birds. An Albatross Bay ill. 
(Biomedea exidans) mounted with the wings expanded, shows ^^ucture 
the most important characters by which a bird is externally of Birds, 
distinguished from other animals. The surface of the body is 
clothed with feathers, which (in the majority of birds), by their 
great size and special arrangement upon the fore-limbs, enable 
these to act as organs of flight. The mouth is in the form of 
a horny beak. A nestling Albatross shows that at this stage of 
its existence the bird is not clothed with true feathers, but with 
soft down, which serves to keep the body warm, although it 
confers no power of flight. An Emu and Apteryx in the lower 
compartment of the case display the exceptional condition (found 
only in a comparatively few members of the class) of birds with 
wings so small as to be concealed beneath the general feathery 
covering of the body, and quite functionless. In the Penguins, 
of which two species are shown in the case, the wings are 
reduced to the condition of fins, and are only serviceable for 
progression through water. 
In the first wall-case the principal facts in the osteology of the 
class are shown. Sections of bones exhibit the large air-cavities 
within ; a complete skeleton of an Eagle, with the bones sepa- 
rated and named, and mounted skeletons of the Ostrich, Penguin, 
Pelican, Vulture, Night-Parrot, Fowl, &c., show the chief modi- 
fications of the skeleton. The Apteryx possesses the smallest, 
and the Frigate-bird the longest bones of the wing, the corres- 
pondence of which can be readily traced by means of the 
c 2 
