THE BIRDS OF SINGAPORE ISLAND 
10 expectation then, tht long shank-like bone or **leg"' in the 
bird does not in any way represent the shin of the man but his 
*' in step**. This shank-like hone is known in ornithology as 
the tarsus although from the point of view of the comparative 
anatomist it is really rather more than the tarsus. 
The wing seems to have hee^n evolved from a forettmb 
that was used in the ambulatory manner common to quad- 
rupeds. It consists of a series of bones, corresponding very 
closely to those in our own hand, w^rist and arm, to which 
are attached the krge flight feathers or quills, The quills 
that grow from the bones of the hand are known as primaries 
and those attached to the forearm (ulna) are called secondaries. 
Both above and below the bases of the quills are strengthened 
by series of small, neatly arranged feathers— ihe upper and 
lower wing-co verts, Tiie * 'elbow" or forward point of the 
bjrd*s wing is the joint corresponding to the wrist in man. 
The tail consists of a series of quill feathers (very much 
like those of the wing-) and again with their bases covered with 
smaller feathers (the upper and lower tail-coverts) arranged 
round a flattened, ploughshare-like bone. In modern birds 
the fcttrices> as the tail quills are called, are arranged in a 
single horizontal series but it seems evident from the study of 
a remarkable fossil bird A}ch{Fopteryx\ that at one time birds 
had a long tail like a lizard, and as in that animal composed of 
a large number of vertebrae. Each vertebra had a pair of 
quill-feathers attached — one each side— and if we imagine a 
telescoping process as happening to this primitive tail we can 
get a fair idea as to how the bird's tai! in its present state was 
evolved. It is not our intention here to discourse on the 
internal anatomy of birds but perhaps a few words as to certain 
salient features will not be out of place. 
The skeleton is remarkable for its rtgidity and pnejinwti- 
city. Both of these conditions can be readily understood as 
suited to a creature of aerial habits. As a famous ornithologist 
once remarked the skull of a bird is a poem in bont — its archi- 
tecture is the frozen musk of morphology, It is in the 
arrangement of the bones in the palate that birds bear pro* 
minent witness to their reptilian ancestor) , 
[20] 
