MOEPHOLOGY OF THE OWLS. 



29 



In the Asionidae, its distal extremities are laterally compressed, and furnished with 

 an oval facet for articulation Avith the coracoid. In some species, the two limbs fail to 

 meet in the middle line, e. y. Speotyto, Glaucidimn, Surnia, whilst in others the 

 degeneration of this region has not proceeded quite so far, the limbs being still united, 

 but by a very slender thread of bone. In the nestling Speotyto it is interesting to note 

 that the furcula is still entire. The backw^ard extent of the furcula varies considerably. 

 In many of the AsionidsB the furcula reaches the inferior and tinterior angle of the 

 carina, and is held in position by strands of connective tissue, no articulation taking 

 place. In others the furcula falls considerably short of the carina, e. y. some species of 

 JSubo, Syrnium, Asio. 



In some cases, e.y. Bubo maximus, the furcula is closely bound to the anterior border 

 of the keel, the union taking place near the middle of the border. The furcula is 

 pneumatic in all the Asiouidae. 



In the Strigidse the furcula articulates with the carina, which at the point of articu- 

 lation has developed a lateral expansion. The furcula differs from that of the Asionidae, 

 not only in the fact of this articulation, but in that the distal ends lack the articular 

 facet for the coracoid. Furthermore it is non-pneumatic. 



The sternum is nearly as broad as long, and bears a well-developed carina. The spina 

 externa is moderately large, but the spina interna is wanting. 



The sternum of the Striges more nearly resembles that of the Falconiformes than any 

 other group. This resemblance, it should be stated, is most marked where comparisons 

 are made between Strigine sterna and those of Accij)itres. The following characters will 

 be found useful in determining between sterna belongmg to these two very different groups. 

 The posterior border of the sternum in the Striges is never entire, and never fenestrated, 

 but always notched. With the exception of the sterna belonging to the Strigidae, and 

 the sternum of Suhua nipalensis (p. 37) of the Asionidae, there are two pairs of notches. 

 The single pair of notches of Snhua are of great size. They lie on either side of the 

 metasternum, and extending forwards to beyond the level of the middle of the posterior 

 lateral process, cause the sternum of this bird to resemble closely that of Microhierax 

 among the Accipitres. The great difference in size, however, renders any possibility of 

 confusion on accoitnt of this resemblance impossible. 



The anterior lateral processes are small and form blimt-pointed projections from the 

 antero-lateral angles of the sternal plate, which are deeply grooved for the origin of the 

 sterno-coracoideus, the groove extending back as far as the last rib articulation. 



The siiina interna is wanting, a deep notch occupying its place. The spina externa is 

 present only in the Asionidae, and here it projects downwards rather than forwards. 



The single pair of notches in the sternum of the Strigidae resemble those of some 

 Accipitres, e. y. Manoldcs, in that they are very shallow, so that the posterior lateral 

 processes pass almost insensibly into the metasternum, being divided therefi-om only by 

 a sinuous line. But the processes are relatively much longer in the Strigidae than in the 

 Accipitres, and the sternum is narrower. 



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, ! L I B R A R Y 



