STUDIES OE THE MACKOCHIBES. 
375 
stand 2, 3, 4, 5, while, as w r e know, in Micropus they stand 2, 3, 
3, 3. 
As existing birds are classified, and were two such forms as 
Micropus and Trochilus classified upon the characters presented 
in their pelvic limbs alone, all I can say is, that to my mind 
there should be no hesitation whatever in placing them in widely 
separated groups, notwithstanding the fact that the myological 
formula of the thigh-muscles is the same. For even when we 
come to examine these very muscles closely we soon discover 
that they are quite differently formed and disposed , which should 
also be taken into consideration in face of the fact of the mere 
presence or absence of parts. 
For the rest, the limb in these two groups of birds to its 
very toe-joints is about as essentially different as are the limbs 
of an Ostrich and a Coot. 
On the Anatomy of the Head. 
Were I asked to pick out any two forms of existing birds from 
any part of the world which present us with the greatest 
number of fundamental differences so far as the anatomy of 
the head is concerned, it would puzzle me, I think, to select 
two more diverse types than a true Swift and a Humming-bird. 
Indeed, from tip of beak to nape it is difficult to find comparable 
characters that show any affinity of the forms in question at all. 
I have already pointed out above the very evident differences that 
are exhibited upon a comparison of the external characters of 
such a Swift as Micropus and any of the Trochili ; while the 
principal differences in the skulls of these birds have been already 
dwelt upon *. And has the day yet arrived when differences 
of the most manifest character in the skulls of birds are to be 
ignored in taxonomy, and set aside as of no value P 
At the present time I have before me upwards of a hundred 
anatomical specimens of Trochili and a great many Swifts ; but 
for a brief resume of some of the distinctive cranial characters let 
us choose a specimen each of Chcetura pelagica and Trochilus 
rufus, and see how they compare in these two types. We find 
these characters to be as follow : — 
* Proc. Zool. Soc. 1885. 
