402 PEOF. T. JEFFEHT PAEKEE ON THE CEANIAL OSTEOLOGY, 



distinct orbitonasal, oculomotor, and abducent foramina, but the fourth nerve goes out 

 through the optic foramen. Thus all the Australasian genera agree in having a 

 distinct foramen for the sixth nevve ; the Moas are peculiar in having the oculomotor, 

 orbitonasal, and abducent foramina sunk in a fossa (fig. 76). 



In the structure of the ethmoid Apteryx stands at one end of the series, the Dinorni- 

 thidee in an intermediate position, and the remaining Ratitae at the other end. In the 

 Moas, as we have seen, the lateral ethmoid extends backwards almost to the optic 

 foramen, its posterior part consisting of the gently sloping inferior aliethmoid, which is 

 continued in front into the obliquely set antorbital. In Aptenjx the place of both these 

 portions is taken by the shell-like aliethmoid, which extends from the optic foramen to 

 the lacrymal, bulging outwards in its whole extent and undergoing a special dilatation 

 immediately caudad of the lacrymal. In the remaining Ratita3 the olfactory cavity is 

 not continued backwards behind the antorbital, the latter springing directly from the 

 mesethmoid and passing outwards and forwards to the lacrymal. In Stntthio and 

 Rhea only the mesial portion of the antorbital is ossified, so that in the dry skull a 

 considerable space is left between its outer edge and the lacrymal. In Dromwtis aud 

 Casuarius the ossification extends to the lacrymal, and the dorsal portion of the bone 

 is hollowed by a deep pit for the lacrymal gland. In Struthio, Rhea, and Casuarius 

 the descending process of the lacrymal bone is merely notched for the lacrymal duct ; 

 ill Vroiiueus and Apteryx it is perforated. 



The postchoanal bar formed by the ventral border of the antorbital is most distinct 

 in the Ostrich and Emu. The mesethmoid is perforated posteriorly, so as to place the 

 olfactory chambers in communication, in the Ostrich, Ehea, and Emu, but not in the 

 Cassowary and Kiwi. In the possession of the triangular process of the mesethmoid 

 the Moas stand alone. 



Leaving Apteryx aside, the chief difference between the Dinornithidse and the other 

 Ratitse as regards the cranial cavity is the greater size of the mesencephalic fossae in 

 the latter. The pituitary fossa of the Moas is most nearly approached by that of Struthio, 

 in which the thickness of the presphenoid gives rise to a broad optic platform, poorly 

 marked in all the other genera. The cerebral fossae are more pointed anteriorly in the 

 other genera and are continued forwards into deep conical olfactory fossae; in this point 

 also it is the Ostrich which approaclies most nearly to the Moas ; its hemispheres are 

 blunter and its olfactory lobes shorter than in the American and Austro-Malayan forms. 



Apteryx agrees with the Dinornithidae in the small size of the mesencephalic fossae, 

 but is quite peculiar in the great proportional size of the cerebral and olfactory fossae. 

 The hemispheres extend backwards over the cerebellum, the cerebellar fossa being 

 therefore pushed backwards and the tentorial ridge made almost horizontak Owing 

 to the great size of the olfactory fossae, the crista galli is nearly as long as the basis 

 cranii from the dorsum sellae to the occipital condyle. 



The premaxilla has the usual structure in all. In the Ostricli alone the palatine 



