THE CEANIAL NEEVES AND LATEEAL SENSE OEGANS OF FISHES. 



221 



17. Fifth sub-orbital. 



18. Anterior extremity of pre-operculum. 



19. 1 Primordial cranium. 20 = the " supra-orbital 

 20./ bands" of Parker (152, p. 129). 



21. " Great fontanelle" (Parker, loc. cit.) 



22. Fused trabeculse ( " inter-trabecula ") . 



23. Parasphenoid. 



24. Metapterygoid. 



25. Syraplectic. 



26. Quadrate. 



27. Cerato-hyal. 



28. Brancliiostegal rays. 



29. Gill arches, with attached muscles, blood 



vessels, and gills. 



30. Fragments of thyroid gland. 



31. Phaiyngeal chamber. 



32. Anterior extremity of opercular chamber. 



33. Retina. 



34. Sclerotic. 



35. Superior rectus -1 



36. Inferior „ I eye muscles. 



37. Internal „ J 



Fig. 4. Transverse section of sense organ 3, supra-orbital canal, from a young Gadus virens. X 240. 

 Details filled in with Zeiss Apochr. Hom. Imm. 2'0 mm., apert. r30, oc. compens. 4, 

 45 mm. 



1. Sensory cells of sense organ. 



2. Glandular cells of same (note periphery of 



organ consisting entirely of gland cells, 2', 

 and centrally the secretion of the latter 

 passing between the sensory cells). 



3. Cupula terminalis (apparently contracted from 



its original attachments). 



4. Nerve of sense organ. 



5. Supra-orbital canal in transverse section. 



6. Blood vessels. 



7. Lateral frontal [i. e. lateral line ossicle 



secondarily fused on to frontal) . 



8. Frontal. 



