676 SHUFELDT—OSTEOLOGY OF THE STRIGES. [Dec. 7, 
does so by a costal rib on the right. None of the ribs thus far 
mentioned bear epipleural appendages. Now, in a specimen of 
Asio wilsontanus, the first pair of tiny free ribs occur upon 
the twelfth cervical vertebra; the next pair are considerably 
larger, while those on the fourteenth have epipleural appendages, 
and both connect with the sternum. 
Strix pratincola also often has a pair of ‘ floating ribs ’’ behind 
the last dorsal pair. In this Owl, too, we find a very large patella. 
All Owls have a notably long fibula, while in S¢vzx it is quite per- 
fect and comes down very close to the condyle of the tibio-tarsus. 
The relative lengths of the bones of the lower extremity are rather 
remarkable in Strix pratincola. In amounted skeleton (18196) in 
the cases of the United States National Museum of this species, I 
find the femur to measure 6.5 centimetres, the tibio-tarsus 11 cen- 
timetres, and the tarso-metatarsus 7.9 centimetres. 
As is now well known, a variety of species of Owls have asymmet- 
rical skulls, an asymmetry that is due largely to a distortion of the 
postfrontal and squamosal regions of the cranium. It may occur,I be- 
lieve, upon either side. Audo virginianus, however, presents us with 
no such character in its skull, and this Owl possesses a lofty superior 
osseous mandible, with the nasal septum completed in bone, all to a 
small space behind. In it, as in most Owls, the lower part of the 
great spongy lacrymal is moulded upon the still larger maxillo- 
palatine beneath ; the last also being a tuberous, spongy mass, of a 
form something like a small chestnut, with the bulbous end to the 
rear. ‘These maxillo-palatines do not meet each other mesially, 
and they rest, on either side, upon the horizontal prepalatine blade 
of the palatine bone (see Plate XII, Fig. 10). 
In the lacrymal region a large foramen exists externally, the 
walls of which are formed chiefly by the lacrymal, the nasal and 
the maxillo-palatine. It passes into the rhinal chamber. As Mr. 
Beddard has already pointed out, the pars plana in all of the Bubo- 
nidine type of Owls is comparatively small and of a thin, plate-like 
structure. It is quite small in. Budo virginianus, and in all of the 
Owls wherein it exists, as we have just described it, it is so turned 
as to form a partial rest for the eye anteriorly, rather than an 
osseous partition between orbit and rhinal space beyond. 
A very small vacuity may exist in the interorbital septum in 
Bubo and some strigine forms related to that genus, but it is of by 
no means a common occurrence. 
