Wo. 1.) NORTH AMERICAN PASSERES. 85 
in its skeleton a faczes peculiar to itself, but often difficult to 
satisfactorily describe. 
In another connection the writer has already presented a view 
of the superior aspect of the skull in Sialia mexicana, so it will 
not be necessary to re-describe it here! Upon the lateral 
aspect of this part of the skeleton in the Bluebirds, we are to 
note the large subelliptical aperture of the external nares, 
and the complete absence of any osseous septum between it and 
the corresponding opening on the opposite side. The superior 
osseous mandible is somewhat curved, tapers smartly to its apex, 
and is possessed of cultrate tomia. Standing as a good-sized 
bony partition, we have a quadrilateral os plana or pars plana 
dividing, as usual, the rhinal chamber from the orbit, while 
in nestling specimens of any of the Sza/za, we find in front of 
this a large and free lacrymal bone, much as it occurs in the 
Corvide ; here, however, this ossicle completely fuses with the 
pars plana by the time the bird has fully matured, which is not 
the case among the Crows.? 
Bluebirds, as is the rule among most, if not all, true 7urdide, 
have capacious orbital cavities, with a very deficient bony septum 
dividing them. This deficiency is due to a sizable vacuity which 
occupies its central part, while the opening for the first pair of 
nerves is unduly large, and encroaches to no small degree upon 
the upper part of the interorbital septum. Notwithstanding 
these facts, in most specimens the foramina rotunda remain 
both distinct and entire. Passing to the posterior lower mar- 
ginal boundary of an orbit, it is seen that neither the sphenotic 
nor the squamosal process in Sza/za is very well developed ; the 
latter being rather the better of the two, projecting out as it 
does over the mastoidal head of the quadrate on either side. 
1 SHUFELDT, R. W., “Notes upon the Osteology of Cinclus mexicanus” #z//. 
Nutt. Ornith. Club, Cambridge, Mass. Vol. VII., No. 4, Oct., 1882, pp. 213-221, 
Fig. B. The same figure is also given in Coues’ Key to North American Birds, 2d 
ed., p. 241. 
2 SHUFELDT, R. W., “On a Collection of birds’ sterna and skulls, collected by 
Dr. Thomas H. Streets, U. S. Navy.” Proc. U. S. Nat. Mus., 1887, pp. 376-387. 
The lacrymal bone in the Raven C. corax sinuatus is alluded to here, but is more 
fully described in a paper by the writer, which we will have occasion to quote further 
on. The morphology of the lacrymal bones stands in some need of more careful 
research among the Passeres, and for the class at large it is subject to a wonderful 
series of variations. To instance this, we have but to compare the lacrymal in such 
forms as Ortyx, Anas, and Sturnella. 
