290 OSTEOLOGY OF TUBINARES AND sTEGANOPODES. 



The part played in the mechanism by the mamillaries has already 

 been described above. 



We find the sphenotic process to be bifid and jutting directly out 

 from the side of the skull ; on the otlier band, the mastoidal process is 

 a crest of bone curling forward. Between tbese two the very wide 

 crotaphyte valley is seen. 



The quadrate is a large, massive bone, with its mastoidal bead com- 

 posed of two prominent ellipsoidal trochlea*, separated from each otlier 

 by an intervening notch. Below tbese the shaft is seen to be rather 

 compressed in an anteroposterior direction, and supports in front at its 

 lower half an unusually formed orbital process. This is a thin, tri- 

 angular plate of bone placed in the vertical plane, and with its apex 

 directed forward. The pneumatic foramen of the quadrate usually 

 occurs on the posterior aspect of the shaft in most birds, but here it is 

 situated to the inner and lower side of this orbital process. 



The pit for the quadrato jugal is cylindrical and deep, and a perfora- 

 tion at its bottom may lead into the hollow of the bone. On the pos- 

 terior aspect of the quadrate we find an irregular facet for the mandi- 

 ble; it looks directly to the rear and stands at the head of a longitudi- 

 nal and deep groove which is found between two similarly placed facets 

 on the foot of the bone. 



Each pterygoid is a trihedral and compressed bone with prominent 

 borders. 



Regarding this skull from a superior view (Fig. 24), we see in it a 

 foramen in the superior mandible near the site of the narial opening of 

 the majoi ity of other birds. From this aspect we also have a good view 

 of the wonderfully perfect craniofacial hinge of the Gannet. 



Posterior to this is a broad, smooth area, very slightly convex, and 

 showing only at its binder half the barest trace of a longitudinal furrow. 

 This surface extends from the cranio-facial hinge to the anterior border 

 of the crotaphyte fossa 1 , while Laterally it is bounded by the margins of 

 the orbits. 



This view also shows the extent and form of these crotaphyte fossa) 

 and how they are separated from each other in the median line simply 

 by an extension backward of a very narrow strip of the general surface 

 that lies beyond them. They are bounded behind by conspicuous and 

 sharpened crests that curl slightly forward, and are best marked later- 

 ally, becoming very low as they near the upper part of the supra occip- 

 ital prominence. 



The under view of the skull reveals a number of interesting points. 

 We find thai the anterior portions of the palatines are parallel to each 

 other, separated by a median cleft of a width equal to either one of 

 them, and which becomes pointed behind. 



Their anterior ends do not merge into the premaxillary beyond until 

 they are well past the points where the maxillaries are inserted. Tbese 

 anterior portions are thin, horizontal plates, being directly continuous 



