MOEPHOLOGY OF THE OWLS. 17 



of relatively large size, and is bounded sujieriorly by the parietal, anteriorly by the 

 alisplienoid, and mesially by the basioccipital, inferiorly by the opisthotic, and 

 posteriorly by the epiotic. The floccular fossa, which is deep and pit-shaped, lies wholly 

 within the pro-otic, but is closed posteriorly by the epiotic. The meatus internus is very 

 shallow. The pro-otic is concealed from view externally entirely by the squamosal, but 

 is widely separated from contact with the hitter by a great air-space — the recessiis 

 tympanlcus stqjerior. 



The epiotic in the skulls now under description is completely ossified, and anchylosed 

 with the supraoccipital. Its relations to the pro-otic are made manifest through fine 

 sutures passing through into the floccular fossa. 



The o2nsthotic has completely fused with the pro-otic and basioccipital, only a trace 

 of a suture remaining visible below the floccular fossa to mark the separation of the two 

 otic bones. Fusion with the basioccipital is complete. A well-defined suture remains, 

 however, to divide the opisthotic from the epiotic and supraoccipital bones. 



The hasisphenoicl, seen from the cranial cavity is still distinct ; seen in section, the 

 suture between itself and the basioccipital is also distinct. Only the inner table of 

 the basisphenoid is, however, represented ; all the rest of this bone has been absorbed 

 to contribute towards the formation of the huge recessns tympanicus anterior. The 

 pituitary fossa forms a basin-shaped pit, which is externally completely surrounded by the 

 air-sinus just described. There is no indication of the ossification of the basisphenoid 

 from separate centres, such as is seen in the Pygopodes, for example. 



The presp/ienoid, if present, is still represented only by cartilage. 



The alisphenoid proves to be an exceptionally interesting bone in the Strigidse. In 

 the young skull of Syrnium, this bone is partly concealed externally by the squamosal, 

 which overlaps its infero-external border. So much as is visible is roughly oblong 

 in form, its long axis extending from the interorbital septum outwards. 



Besides being overlapped by the squamosal, it is embraced above by the orbital process 

 of the frontal, and below by the basisphenoid. Its precise form can best be studied 

 from the inside of the skull. Viewed from this aspect, it will be found somewhat lingui- 

 form in outline, and to send inwards from its anterior border a long arm -like process 

 which arises from a swollen base. But little change takes place in the form of this 

 bone in later development ; the space which is left above this arm-like process is filled in 

 by the orbital process of the frontal and the orbito-sphenoid. 



The relations which obtain between the alisphenoid, parietal, squamosal, and frontal 

 are discussed on p. 18. They are especially worthy of note, seeing that they dilTer 

 completely from those which obtain in Speotyto, for example. 



The orbito- and pre-sphenoids have not yet begun to ossify. 



The mcsethmold (PI. 2. fig. 7 a) is yet only partly ossified. In the skulls in the 

 Museum Collection it forms a Hnguiform plate projecting downwards from the skull- 

 roof to the parasphenoid. Its anterior border is straight, its posterior border convex. 

 The dorsal border is expanded into an oval horizontal plate visible, in the yoimgest 

 skulls, on the surface of the skull, where it appears wedged in between the frontals, 

 and overlapped on either side by the nasals and nasal processes of the premaxilla. 



SECOND SERIES. — ZOOLOGr, VOL. IX. 8 



