THE SKULL. 409 



and in front of the articular surface for the 

 quadrate. 



V. The orbit is a very large depression in the side 

 of the skull, which lodges the eyeball ; it is 

 bounded above by the frontal bone ; in front, 

 by the frontal and lacrymal 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 all- 

 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 and covered by a 

 membrane- bone, the rostrum, which forms the 

 anterior part of 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 



