32 NERVE COMPONENTS OF BONY FISHES. 



y. — TJie Infra-Orbital Canal. 



This canal passes ventrad and slightly caudad and is 

 enclosed at once by the most dorsal of the post-orbital 

 bones. Its course is very short, for as soon as it has 

 passed this bone it opens out and disappears. This bone 

 is rather massive, much more so than any of the other 

 bones of the orbital ring. 



There are no pores in this short section of the canal and 

 but one sense organ. The infra-orbital canal is absent 

 from the most caudal edge of the orbit to a point a little 

 beyond its ventral edge, where it resumes. This short por- 

 tion of the infra-orbital canal we shall call the post-orbital 

 section, the pre-orbital portion, the lachrymal section. 



It is interesting to note that the entire orbital ring of 

 bones in Menidia is very much reduced. In view of the 

 fact that the lateral line organs of the head normally lie in 

 bony canals and that, even if the canal is not entirely 

 enclosed in bone, there is a tendency to form bridges of 

 bone over the organs themselves (as, for example, in the 

 supra-orbital canal), it would seem reasonable to conclude 

 that the absence of that portion of the infra-orbital canal 

 which is normally enclosed in the bones of the orbital ring 

 is correlated with the reduction of those bones. 



The portion of the infra-orbital line which lacks the 

 canal is represented by a series of naked sense organs 

 which in shape resemble the terminal buds more than 

 they do the canal organs. Those near the open ends of 

 the canals are larger than those in the middle of the naked 

 series. They are all innervated, however, by the coarse 

 fibres of the r. buccalis belonging to the acustico-lateralis 

 system. 



There are fifteen sense organs in the infra-orbital series, 

 the first five in the lachrymal section of the canal, nine 

 naked organs in the ventro-caudal quadrant, and one canal 

 organ in the short post-orbital section. The latter and 

 the last two naked organs are innervated by the r. oticus, 

 all of the other organs by the r. buccalis. 



