STUDIES OE THE MACEOCHIBES. 
367 
On the throat of Swifts and Swallows the feathering covers 
the entire area, while in Humming-birds the median naked space 
of the neck is continued almost up to the base of the inferior 
mandible. 
Again, Nitzsch noticed the naked “nape-space [see his figure] 
beneath the long cornua of the hyoid bone,” but “ could not deter- 
mine with precision ” whether or no it was a constant character 
for the pterylography in the Trochili. My investigations con- 
vince me that it is a constant character in them, and, further, 
that it is never present in the Swifts nor Swallows. If any one will 
take the trouble to pluck a Humming-bird and note, in the 
natural position of its head, that the back of the head comes 
very close to the body, he will see at once how this naked space 
has come to be present there. 
The arrangement of the pterylse upon the ventral aspects of 
all of these birds is more or less alike, being apparent modifica- 
tions of some Passerine type ; but not so with the spaces upon 
the dorsal aspects, for here we find that the true differences 
among them come in (compare Hitzsch’s figures). And we must 
remember that Nitzsch, in speaking of the pterylography of the 
Macrochires, was forced to admit that : — “ In this family I place 
the two genera Cypselus and Trochilus, which, indeed, present 
but little external similarity, but are very nearly allied in the 
structure of their wings ” (p. 86). To the near alliance on 
account of the latter character we will revert later on. 
In the first part of this memoir I have attempted to point out 
such differences as exist between the pterylography of a Swift 
and a Swallow, so it will not be necessary to enter so fully upon 
the details again here. Be it borne in mind, however, that, 
upon this dorsal aspect of the two, in both the humeral tract 
crosses obliquely at a point opposite the middle of the humerus 
of the arm ; in Trochilus, on the other hand, it is over the 
head of the humerus. Swifts and Swallows both possess a femoral 
tract ; whereas it is absent as a rule (and, for all that I know 
to the contrary, always) in the Humming-birds — certainly so in 
Trochilus . 
In Swifts the “ spinal tract ” connects the capital area behind 
with the oil-gland, but just opposite the shoulder-joints bifur- 
cates ; the bifurcations are as wide as the original tract, and 
after passing the middle of the back they converge again, and 
unite at a point over the anterior end of the sacrum. Thus we 
