STUDIES OF THE MACROCHIRES. 



361 



I find, however, that the basibrauchials are auchylosed into one 

 piece, while the glosso-hyal and the eerato-hyala are apparently 

 not ossified even in the adult Martin, 



Several skeletons of PetrocJielidon lunifrons have been carefully 

 prepared by me from specimens of tlie bird which T collected 

 a year ago at Fort AYingate, 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. 



GTielidon erytlirogaster in tliis part of its skeleton probably 

 typifies the Hirund'ine 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 !^I^uU of Chelidon 

 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 giosso-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 



