SEC. IV ANA TOMY OF BIRDS 235 



with surrounding bones in the adult. It is wedged into the very 

 midst of the cranial bones proper, with its body in the middle line 

 below, next in front of the basioccipital, and its wings spread on 

 either side in the orbital cavity. A sphenoid consists essentially 

 of the basisphenoid, or main part of the bone (Fig. 62) ; the pair 

 of aUsphenoids or "wings," one on either side (Figs. 70, 71, as); 

 the obscure presphenoid (ps) in the middle line in front of and 

 above the main body; and the pair of small orbitosphenoids, 

 which are in fact the wings of the presphenoid. The body is 

 usually covered in by the underflooring of the basitemporal ; it 

 is a flat triangular plate, produced more or less forward in the 

 middle line as the lasisphenoidal rostrum, or beak of the skull. 

 This rostrum (ap to rbs in Fig. 70) is an important thing. It forms, 

 in fact, the central axis of the base of the skull ; with the meseth- 

 moid plate the inferior border of the interorbital septum, usually 

 thickened by the underflooring of the parasphenoid (Fig. 70, rbs). 

 The rostrum often bears on each side a basipterygoid process {ap), — a 

 smooth facet with which the pterygoid articulates. These processes 

 may be very strong, and far back on the basisphenoid body, when 

 the pterygoids articulate with them near their own posterior ends, 

 as in the struthious birds and tinamous (Fig. 75, Up) ; or they may 

 be further along on the rostrum, and the pterygoids then articulate 

 near or at their fore -ends. The rostrum may be produced far 

 forward, beyond the maxillopalatines and vomer even, as in an 

 ostrich ; or it may bear the vomer at its end ; or may be embraced 

 by forks of the vomer; the palatines may glide along it, or be 

 remote from it on either side. In any event, whatever its produc- 

 tion, whatever part may be ethmoidal, or basisphenoidal, or para- 

 sphenoidal thickening, pterygo-faceting, etc., this "beak" of the 

 basisphenoid is always in the axis of the base of the skull, and 

 at the bottom of the interorbital plate ; it may be horizontal, or 

 obUquely ascending forward ; and the variety of its relations with 

 the pterygopalatine and vomerine mechanism furnishes important 

 ■zoological characters, as we shall see when we come to treat of 

 palatal structure particularly. Just at the base of the beak, where 

 it widens into the main body of the bone, may commonly be seen, 

 coming from between the sphenoidal body and the lip of the basi- 

 temporal underflooring, the orifices of the Eustachian tubes, and 

 often also the anterior ends of the carotid canal. If a bristle, 

 passed into a questionable foramen here, comes out of the ear, it 

 has gone through the Eustachian tube ; if it comes out below the 

 ear, on the floor of the skull, outside, it has run in the carotid 

 canal. The extent of the aUsphenoids (Figs. 70, 71, as) cannot 

 be determined in old skulls. They lie at the back lower border 

 of the orbital cavity, closing in most of the brain-box that is 



