380 SKELETON OF THE FOWL 



by the frontal and laerymal bones, the latter 

 of which is produced downwards at its anterior 

 end into a slender curved process. Behind, 

 the orbit is bounded by the frontal with 

 its post-orbital process, and by the ali- 

 sphenoid ; and on the inner side it is separated 

 from the orbit of the other side by the inter- 

 orbital septum, a thin vertical plate of bone, 

 formed by the coalescence of the pre-sphenoid 

 and orbito-sphenoid behind, and the mes- 

 ethmoid in front and above. The lower edge 

 of the septum is thickened, forming the ros- 

 trum, and is covered by a membrane-bone, the 

 para-sphenoid. 



Below, the orbit is very incomplete ; its 

 outer margin is formed by the slender zygo- 

 matic arch, and its floor, nearer the middle 

 line, is formed in part by the palatine and 

 pterygoid bones. 



vi. The foramen of exit for the olfactory nerves is 

 a median opening, at the anterior end of the 

 cranium, and is continued forwards as a 

 horizontal slit, between the inter-orbital sep- 

 tum and the frontal bones. 



vii. The optic foramen is a large median hole in 

 the orbito-sphenoid bones, opening into the 

 posterior part of the orbits, and continued 

 forwards as a semicircular notch in the inter- 

 orbital septum. 



viii. The foramina of exit for the third and fourth 

 nerves are small holes, immediately to the 

 outer side of the optic foramen, and sometimes 

 confluent with it. 



d. The dorsal surface of the cranium. 



The dorsal surface of the cranium is rounded, 

 and , formed almost entirely by the parietal and 

 frontal bones. It is broad behind, narrower in 



