CLASSIFICATION, AND PHTLOaENT OF THE DINOENITHIDiE. 385 



Another interesting embryonic character is the occasional presence of a small pit or 

 foramen situated in the middle line at the junction of the rostrum with the basitem- 

 poral platform, and at the level of the anterior borders of the basipterygoid processes ; 

 when patent it leads into the pituitary fossa. This is a remnant of the anterior 

 hasicranial fontanelle {a.l.cr.fon.) through which the pituitary pedicle passes from the 

 pharynx to the cranial cavity. Its retention in the adult is somewhat remarkable, as 

 ia Apteryx (24) it is completely covered by the rostrum, and only visible when, in the 

 young skull, the latter is stripped from the underlying cartilage. 



The rostrum as seen from below has the appearance of a more or less cylindrical rod 

 of bone ; actually it is doubtless crescentic in section, as in other birds. It is frequently 

 slightly constricted towards its junction with the basi temporal platform, its middle 

 region is often much compressed and keel -like, and its anterior end is pointed. It will 

 be further considered in connection with the ethmoidal region, but one remark must be 

 made here as to its position. It usually lies nearly or quite in the same horizontal plane 

 as the basitemporal ; but in Dinornis the two are set at an obtuse angle (about 150°) 

 with one another, thus giving rise to the deflected beak characteristic of that genus. 



iv. The lateral surface of the cranium. (Plate LVI. fig. 3 ; Plate LVII. fig. 7 ; 

 Plate LVIII. fig. 13 ; Plate LIX. fig. 18 ; Plate LXI. figs. 35-46). 



The tympanic cavity is a deep depression bounded behind by the paroccipital 

 process, above by the squamosal prominence, and mesially by a greatly pitted surface 

 furnished by the exoccipital and pro-otic bones. It is continued downwards and 

 forwards into a sort of pocket, the anterior tympanic recess, bounded in front by a 

 thin, oblique, quarter-cylinder of bone, the pretemjioral wing (figs. 6 & 1 3, pr.temp.w.). 

 A young skull shows this process to be part of the combined basisphenoid and 

 basitemporal ; probably, as in other birds, it is formed by the latter. In some cases 

 the anterior tympanic recess becomes largely filled up with spongy bone and thus 

 reduced to a quite insignificant cavity; it is best marked in young skulls of 

 Anomalopteryx didiformis, but is also large and conspicuous in Mesopteryx casuarina 

 and some other species. 



The squamosal prominence {sq.prm.) is a thick outstanding mass, convex above, 

 deeply concave below, and formed by the squamosal bone (mastoid, Owen), which 

 articulates mesially with the parietal, exoccipital, alisphenoid, and pro-otic. It is 

 produced downwards into the zygomatic process (mastoid process, Owen, zyg.pr.), 

 which, in the entire skull, lies immediately external to the quadrate, is directed 

 slightly forwards, and is sometimes bifid (fig. 3) ; it varies considerably in length. It 

 is continued upwards on to the lateral surface of the squamosal by a slightly wavy, 

 subvertical posterior temporal ridge [post. temp. r.), the dorsal end of which joins the 

 inferior temporal ridge described below (figs. 3 and 13). 



The margin of the tympanic cavity varies in form : in Dinornis (fig. 35) its dorsal 

 edge, furnished by the squamosal, forms an even curve with its posterior edge, furnished 



