230 THE DOG-FISH. 



iii. The foramen for the third nerve is a small hole 

 in the inner wall of the orbit, about a quarter 

 of an inch behind the optic foramen and a 

 little above it. 



iv. The foramen for the fourth nerve is a very 

 small hole near the dorsal border of the inner 

 wall of the orbit, vertically above the optic 

 foramen, or very slightly behind this. 



v. The foramen for the fifth and seventh nerves is 



a large hole at the posterior and ventral angle 

 of the orbit, immediately in front of the audi- 

 tory capsule. Through it the main branches 

 of the fifth and seventh nerves, and also the 

 sixth nerve, enter the orbit. 



vi. The aperture of the inter-orbital canal is a 

 small round hole in front of and a little 

 below the foramen for the fifth and seventh 

 nerves, and below and behind the foramen 

 for the third nerve. The canal traverses the 

 base of the skull, and places the orbital blood 

 sinuses of the two sides in communication 

 with each other. 



vii. The foramen for the hyoidean artery lies a 

 little in front of, and slightly below, the 

 opening of the inter-orbital canal. Through 

 it the hyoidean artery enters the skull. 



viii. The foramina for the ophthalmic branches of the 

 fifth and seventh nerves. These nerves enter 

 the orbit through two holes near its hinder 

 end, just in front of the auditory capsule, and 

 above the foramen for the main branches of 

 the fifth and seventh nerves : the aperture for 

 the ophthalmic branch of the seventh nerve 

 is the larger of the two, and is placed slightly 

 above and behind that for the fifth. From 

 these apertures shallow grooves run forwards 



