THE SUPRA-ORBITAL TRUNK. 199 



in the angle between the vertical plate and the lateral 

 wing, parallel with the slender supra-orbital cartilage and 

 the dorso-lateral edge of the massive internasal cartilage. 

 At the point where the branch so. g for the second canal 

 organ is given off the internasal cartilage spreads out 

 laterally under the frontal bone, so that the supra-orbital 

 trunk lies in a canal bounded above by the frontal bone and 

 on all other sides by the cartilage. This lateral projection 

 of the internasal cartilage is covered on its cephalic and 

 lateral aspects by the highly developed par-ethmoid ossifi- 

 cation and both the cartilage and its investing bone imper- 

 fectly enclose the caudal part of the olfactory sac. From 

 that portion of the par-ethmoid which lies behind the olfac- 

 tory fossa a V-shaped tongue of bone extends into the sub- 

 stance of the internasal cartilage to form a partial bony 

 wall to the canal which contains the olfactory nerve, and 

 a similar tongue farther dorsad to form the floor of the 

 canal containing the supra-orbital trunk, so that this trunk 

 for some distance before it emerges into the olfactory fossa 

 lies in a deep canal bounded above by the frontal and 

 below by the par-ethmoid. 



It emerges at about the same transverse level as the 

 oifactor}^ nerve, but by a separate foramen farther dorsally, 

 previously, however, giving off a very slender nerve {so. 

 id), which turns ventrad and passes into the olfactory 

 fossa by a separate foramen in the par-ethmoid bone and 

 then runs cephalad along the lateral face of the olfactory 

 sac, where it finally joins one of the dorsal twigs of the r. 

 maxillaris V. It probably supplies the caudal (non- 

 sensory) portions of the walls of the olfactory sac. 



Immediately upon the emergence of the trunk from its 

 canal a fine-fibred branch {so. ii) separates and goes at 

 once to the skin mesally of the post-nasal aperture. The 



