STUDIES OF THE MACROCHTRES. 



359 



that exemplifies all the characteristics which pertain to tlio 

 Hirmidine skull generally. 



Its superior osseous mandible is very broad at tlie 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. Tiie 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 JProgne by other 

 anatomists (' Science,' N. T., 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 pre maxillary 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 tliat 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. 



For 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, 



