STliUCTURE OF BIRDS. 
23 
■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. 
Bay No. III. is devoted to the class of Birds. An Albatross Bay III. 
(JDiomcdea exulans) mounted with the wings expanded shove's ^^^^^^ 
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, Avhich 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, tlie 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, Xight -Parrot, Fowl, &c., show the chief modi- 
fications of tlie skeleton. The Apteryx possesses the smallest, 
and the Prio-ate-bird the lono-est bones of the win^, the corres- 
pondence of which can be readily traced by means of the 
labels attached to them. The under surfaces of the skulls of 
various birds are shown with the different bones coloured to 
indicate their limits and relations ; these being followed by a 
series of the different types of sternum or breast-bone. 
The second wall-case contains further illustrations of the 
anatomy of birds, including a series arranged to show the general 
characters of the eggs of this class, as exemplified in their struc- 
ture, number, form, size, texture of surface, and colour. In the 
dipper part are a series of wings of birds displaying the form 
