STUDIES OE THE MACRO CHIRES. 
361 
I find, however, that the basibranchials are anchylosed into one 
piece, while the glosso-hyal and the cerato-hyals are apparently 
not ossified even in the adult Martin. 
Several skeletons of Petrochelidon lunifrons have been carefully 
prepared by me from specimens of the bird which T collected 
a year ago at Fort Wingate, New Mexico, and they are now 
at hand. So far as the skull and hyoidean apparatus of this 
Swallow are concerned, we might almost cover the ground of our 
description by saying that in these parts the bird is the veriest 
miniature of Progne ; and, indeed, so true is this, that any detailed, 
description is rendered quite unnecessary. 
Two points it will be well to note, however, for I believe, com- 
paratively speaking, the cranial capacity in Petrochelidon is 
relatively larger than it is in Progne ; and although the palatines 
are very much of the same shape, the postero-external angles in 
the former are more inclined to be rounded than truncated as they 
are in Progne. 
Ghelidon erythrogaster in this part of its skeleton probably 
typifies the Hirundine skull (PI. XXI. figs. 21, 23). 
In it the superior osseous mandible is very broad at its base, and 
the postero-external angles of the maxillaries have a tendency to 
project a little. The frontal region is more than usually narrow 
between the upper margins of the orbits. Laterally, we note that 
the vacuities in the interorbital septum are usually larger than in 
other Swallows, though yet but two in number, and of the same 
general outline. One thing characteristic of the skull of Ghelidon 
is its uncommonly minute occipital condyle ; I cannot recall at 
this moment any bird of the size of this Swallow which possesses 
this feature in anything like such diminutive proportions. Its 
pterygoids and the quadrato-jugal bars are also wonderfully 
slender osseous rods. 
Agreeing almost exactly with the mandible in Progne , save in 
size, this bone in our Barn-Swallow requires no special mention. 
In the hyoidean arches, however, it would seem that ossification 
is regularly extended to the glosso-hyal and the cerato-hyals, 
which was not the case, as we will remember, in the Martin. 
Passing to the genus Tachycineta , we meet with a skull, in 
either species representing it ( T . bicolor , T. thalassina), which, 
although essentially Hirundine in all particulars, yet bears a closer 
resemblance to some of our other Oscines, not Swallows, than any 
