STUDIES OE THE MACROCIIIRES. 
359 
that exemplifies all the characteristics which pertain to the 
Hirundine skull generally. 
Its superior osseous mandible is very broad at the base, but 
promptly tapers to a sharp and somewhat depressed tip anteriorly, 
while all this portion of the skull is much compressed in the ver- 
tical direction. The form of the external narial apertures can 
best be appreciated upon a superior aspect, and are seen to be 
long, elliptical openings placed longitudinally. Through either 
oue of them we may discern the upper surface of the anterior 
part of the palatine of the corresponding side. The lateral free 
edges of this mandible are sharp and turned downwards, while 
the maxillary on either side is a horizontal plate fully three times 
as broad as the slender jugal bar that continues this infraorbital 
rod to the quadrate. We find no projecting processes from the 
lateral margins of any part of this osseous superior mandible as 
have been erroneously figured for the skull of Progne by other 
anatomists (‘ Science,’ N. Y., No. 223, fig. 3). Just anterior to 
the frontals, and posterior to the external narial apertures, there 
exists a subtriangular area of bone on the top of the mandible, 
which is formed by the proximal portion of the premaxillary and 
the nasal bone on either side. In the adult skull, of course, the 
sutural boundaries of these bones have been absorbed, but by 
holding the skull up to the light the proximal end of the pre- 
maxillary, and what was the median margin of a nasal, and finally 
the anterior limit of the corresponding frontal bone can all be 
easily distinguished, while the small triangular space they cir- 
cumscribe, is also of bone, but considerably thinner than the 
other parts mentioned. In all Swifts that I have examined this 
thinner portion on either side has become absorbed, and a little 
triangular opening is found at the site instead. My explanation 
will be made quite clear by turning to Plate XXI., and com- 
paring figures 22 and 23 ; in figure 23 at x is shown the 
thinned portion, while in the Swift’s skull, figure 22, an opening 
actually takes its place on either side. Of course, in a skull so 
vastly different from the Cypseline skull as the Humming-bird’s 
is, no such comparison as this is necessary. 
Por the rest of the superior aspect of the skull in Progne we 
find the frontal region narrow between the orbital margins, the 
posterior edges of which latter are sharp, thin, and somewhat 
tilted upwards. The parietal region is smooth and rounded, 
