SKELETON OF THE WILD DUCK. THE SKULL. 317 



from a different centre from that forming the squamosal, but 

 in the adult is completely fused with it. 



The orbit forms a large more or less hemispherical cavity 

 which lodges the eyeball. It is separated from its fellow of 

 the opposite side by an imperfect partition, the interorbital 

 septum. In the young skull it is seen to be bounded above by 

 the frontal, with which the lachrymal (fig. 60, 7) is fused 

 anteriorly, forming a large backwardly-projecting process \ 

 while behind it is bounded by the alisphenoid. The inter- 

 orbital septum is formed by the ossification and coalescence of 

 the mesethmoid in front, with the orbitosphenoid behind, 

 and the rostrum below. The boundary of the orbit below 

 is very imperfect, the zygomatic arch being incomplete. 



The interorbital septum is pierced by the very prominent 

 optic foramen (fig. 60, B, 2), just behind which are the two 

 much smaller foramina for the exit of the oculomotor and 

 pathetic (fig. 60, B, IV) nerves, the more anterior being that 

 for the oculomotor. 



Above and slightly in front of the optic foramen is a 

 median opening, the olfactory foramen. This leads into 

 the cranial cavity behind, and in front is continued forwards 

 as a groove between the interorbital septum and the frontal. 



(2) THE FACIAL PART OF THE SKULL. 



This includes the olfactory capsule and associated bones, 

 and the upper jaw. 



The bones associated with the olfactory capsules are the 

 nasals and vomer. The nasals (figs. 59 and 60, 5) lie on the 

 dorsal surface immediately in front of the cranium, and are 

 separated from one another by the nasal processes of the pre- 

 maxillse. Each is completely fused in the adult with the 

 corresponding maxilla and premaxilla, the three bones together 

 forming the boundary of the anterior nares. The vomer (fig. 

 60, 19) is unpaired and forms a small median vertical plate 



