CLASSIFICATION, AND PHTLOGENY OF THE DINOENITHID^. 401 



before backwards, reaching well in advance of the optic foramen ; the temporal ridge 

 is strong, and there is a mid-temporal ridge at about the junction of the middle and 

 posterior thirds of the fossa. 



The comparative size of the orbit constitutes, as already remarked, one of the most 

 striking differences between the Moas and Kiwis and the other Ratitae. In the latter 

 the orbits are separated from one another by a median vertical plate of bone, the 

 interorbital septum, represented in the DinornithidiE only by the wall between the 

 jtresphenoid fossae and wholly absent in yi^;^er^A'. In an adolescent skull of ^^fa the 

 postei'ior third of the septum is formed by the presphenoid, the anterior two thirds by 

 the mesethmoid. There is thus produced an almost straight mesial wall to the orbit, 

 passing above and behind into the arched upper and posterior wall, which is formed 

 above by the orbital plate of the frontal, below by the alisphenoid. In the Dinor- 

 nithida?, there is no clear distinction between the mesial and the postero-dorsal wall of 

 the orbit, the two passing insensibly into one another ; the anterior part of the mesial 

 wall is formed by the inferior aliethmoid, owing to the backward extension of the 

 olfactory capsules between the eyes, and the presphenoid is limited to a small area 

 below the optic foramen. In Apteryx the last trace of the interorbital septum dis- 

 appears, the swollen aliethmoids reaching back to the optic foramen. 



The optic foramina are close together in all the more typical Ratitse, being separated 

 from one another in front by the edge of the interorbital septum, which is very thin in 

 all but Struthio ; the adjacent foramina show, however, considerable variations. In 

 the Ostrich (fig. 71) the oculomotor foramen (iii & vi) lies immediately behind the 

 optic and is contiiuied into the interior of the skull by a groove, into the floor of which 

 the canal for the sixth nerve opens, the oculomotor and abducent nerves having there- 

 fore a common entrance into the orbit. The internal ophthalmic artery apparently 

 goes out separately by the foramen marked a. The small foramen for the fourth nerve 

 (iv) lies just above that for the tliird, and the orbitonasal foramen (v^) is an oblique 

 passage just behind it. In a young specimen the foramina for the third, fourth, and 

 sixth nerves are represented by an oblique cleft communicating with the optic foramen. 

 The trigeminal foramen for the second and third divisions of the fifth nerve may be 

 divided by a narrow vertical bony bar. 



In Eliea (fig. 72) the oculomotor foramen (iii and vi) is immediately behind and below 

 the optic, and the canal for the sixth opens just within its margin ; below and in front 

 of it is an equally large aperture (a), which probably transmits the internal ophthalmic 

 artery. The oculomotor and pathetic nerves enter through very oblique foramina (iv, v') 

 in the usual positions. In Dromceus (fig. 73) the sixth nerve (vi) has a special foramen 

 below the oculomotor (iii). In Cusuarius (fig. 74) tlie third nerve makes its exit 

 through a luitcli (iii) in the posterior margin of the optic foramen, the sixth (vi) 

 through a special foramen ; a notch [a) in the ventral border of the optic foramen 

 possibly transmits the internal ophthalmic artery. In Ajjferi/w (fig. 75) there are 



