OSTEOLOGY OF BIRDS 



15 



In Cathartes a . septentrionalis the pars plana, 

 upon either side, is situated considerably behind the forepart of the 

 mesethmoid, the anterior margin of which latter is sharpened and 

 slopes from above, downward and backward. 



Still confining our attention to the lateral aspect of the skull, it 

 is to be observed that the temporal fossa is much restricted and 

 rather shallow, while the sphcnotic and squamosal processes are 

 moderately developed and of about equal length. 



The zygoma is a stout bar of bone, showing but faintly the sutural 

 traces among its original elements. Between quadrate and pars 

 plana it is quite straight; it is then bent slightly downward to pass 

 forward to the denary process of the premaxillary. At its proxi- 

 mal end a peglike process, placed at right angles to the continuity 

 of the bone, is intended for articulation with a corresponding socket 

 on the outer side of the quadrate [pi. 6, fig. 9]. 



Another notable feature upon this aspect of the skull is the great, 

 gaping aperture to the internal ear; indeed, so exposed is this in the 

 dried cranium, that the surrounding osseous walls offer no impedi- 

 menta to our looking through the short Eustachian tube, or even 

 into the semicircular canals. 



Passing next to the base of the skull in the Cathartidae, we find 

 the foramen magnum subcircular in outline and moderately large. 

 The condyle is usually very well developed, and distinctly notched 

 in the middle line upon its upper surface. The lower arcs of the 

 'bony rims of the external aural openings are produced downward 

 below the general surface, upon either side, and we are to observe 

 that the basitemporal area is very distinctly defined, being triangular 

 in outline and usually small. Its angle in front underlaps the large, 

 single anterior aperture to the Eustachian tubes, while the lateral 

 angles are frequently drawn downward as prominent processes. 

 These latter are markedly conspicuous in such forms as the condors, 

 Gymnogyps, and Cathartes a. septentrionalis, 

 while in Catharista they are merely low ridges of no particular note. 



Often in the skulls of subadult specimens of Cathartes a. 

 septentrionalis we find the Eustachian tubes unprotected 

 by bone in front, the passage being an open, gaping gutter, upon 

 either side, extending from the ear to the base of the rostrum. 

 Birds of several years of age may exhibit this feature in Cathartes, 

 and it probably obtains in the condors. 



Inferiorly, the sphenoidal rostrum is rounded and rather broad 

 at its base, but as we follow it forward, it is seen to gradually taper 



