THE ANATOMY OF BIRDS. — OSTEOLOGY. 



159 



thickened by the underflooriug of the parasphenoid (fig. 70, rhs). The rostrum often bears 

 ou each side a hasipterygoid process {ap), — a smooth facet with which the pterygoid artic- 

 ulates. These processes may be very 

 strong, and far back on the basisphenoid 

 body, when the pterygoids articulate with 

 thein 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 maxillo-palatines 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 ou 

 either side. In any event, whatever its 

 production, whatever part may be eth- 

 moidal, or basisphenoidal, or parasphe- 

 noidal thickening, pterygo-fiiceting, etc., 

 this " beak " of the basisphenoid is 

 always in the axis of the base of the 

 skull, and at the bottom of the inter- 

 orbital plate ; it may be horizontal, or 

 obliquely ascending forward; and the 

 variety of its relations with the pterygo- 

 palatine and vomerine mechanism fur- 

 nishes 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 

 basitemporal underflooring, the orifices 

 of the eustachian tubes, and often also 

 the anterior ends of the carotid canal. 

 If a bristle, passed into a 

 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 alisphenoids (figs. 70, 71, ««) can- 

 not be determined in old skulls. They lie at the back lower border of the orbital cavity, clos- 

 ing in most of the brain box that is not foreclosed by the ft-ontal bone. You will always find 

 at the back of the orbit, close to the mid-line, and rather low down, the very large ojjtic fora- 

 mina (any figs., 2) ; alisphenoid should not extend in front of these orifices. A little below and 

 behind the optic foramina, and much more laterally, not far from the quadrate itself, is a con- 

 siderable foramen, quite constant, for transmission of the inferior divisions of the fifth (trigeminal 

 or trifacial) nerve. This is the foramen ovale (any figs., 5) ; it is either in the alisphenoid, or 

 between that bone and the prootic ; it must not be mistaken for one of the several smaller holes, 

 usually seen close about the optic foramen, which transmit the nerves (oculo-motor, pathetic. 



.?.<?. 



Fig. 71. —Ripe chick's skull, in profile, X 3 diameters; after- 

 Parker, px, premaxillary ; aln, ali-nasal cartilage; en, septo- 

 nasal ; n, nasal bone ; I, lacrymal ; /je, perpendicular plate of 

 ethmoid, as in fig. 70; ps, presjjhenoidal region; ns, ;ilisphe- 

 noid ;/, frontal ; p, parietal ; s?, squamosal; so, superoccipital ; 

 eo, exoccipital; oc, occipital condyle; st, the cross-like object, 

 the stapes, whose foot fits fenestra ovalis, see fig. 83; q. quad- 

 rate; pg, pterygoid; qj, quadrato-jugal; ./, jugal; im, palatine; 

 mx, maxillary. In the mandible: d, dentary; su, surangular; 

 a, angular; ar, articular; iap, internal angular process ; pap, 

 questionable posterior angular process. 2, optic foramen ; 5, foramen ovale, 

 for inferior divisions of the 5th nerve. (Compare fig. 70. ) 



