220 ME. F. J. COLE ON THE STRUCTURE AND MORPHOLOGY OF 



Mx.Mn. Maxillo-mandibulav trunk (trigeminus). 

 N. Autei'ior and posterior narial openings. 

 Na. Nasal portion of the supra-orbital canal. 



0. Opercular fold. 

 O.L. Optic lobe. 



Olf. " Olfactory lobe." 

 PcT.F. Pectoral fin. 



P.F. Post-frontal or sphcnotic portion of the infra-orbital canal. 

 Pzr.F. Pelvic fin. 



P.O. Pit organs or sensory follicles. 

 P.Op. Pre-opercular portion of the hyomandibular canal. 



P.T. Post-temporal or supra-scapular portion of the lateralis canal. 

 Sb.O\ First sub-orbital or lachrymal portion of infra-orbital canal. 

 Ss.O-''. Posterior sub-orbital portions of infra-orbital canal. 

 S.C. Supra-orbital sensory canal (blue). 

 S.Cm. Commissure between the two supi'a-orbital sensory canals. 

 S.O. Superficial ophthalmic nerve trunk (= lateral line and trigeminal portions). 

 /S.O'. Superficial ophthalmic lateral line nerve. 

 S.O". Superficial ophthalmic or first division of the trigeminus. 

 S.O^. Branch of -S.O.' to sense organ 4 of the supra-orbital canal. The two twigs probably 



supply pit organs. 

 S.OK Branch of S.O.' to pit organ (?). 

 S.Q\ Branch ol S.O.' to skin. 



S.O^. Anterior termination of S.O.- which has become separated from the lateral line nerve. 

 Sq. Squamosal or pterotic portion of the infra-orbital canal. 

 S.T^~^. Supra-temporal or extra-scapular portions of the lateralis canal. 

 V. Vagus nerve with compound (?) ganglion. 



1. Olfactory tract, peduncle, or "nerve." 

 II. Optic nerve. 



V.-VII. Trigemino-facial ganglionic complex (adult condition), with portions of its two roots. 



The numbers denote the sense organs and dermal tubules of the respective sensory canals. 



Plate 23. 



Fig. 3. Transverse section of the head of a young adult Gadas virens, passing through the eye posterior 

 to the lens, x 27. Drawn with camera. 



1. Supra-orbital sensory canal. 



2. External aperture of the 4th dermal (com- 



missural) tubvile of supra-orbital canal. 



3. Superficial ophthalmic lateral line nerve. 



4. Branch of above [=8.0.' of Fig. 2) to sense 



organ 4 of supra-orbital canal (note its 

 condition on the other side). 



5. Ophthalmicus superficialis trigemini. 



6. Infra-orbital sensory canal. 



7. Upper and lower rami of inner buccal lateral 



line nerve. 



8. Superior maxillary Vth. 



9. Inferior maxillary Vth. 



10. Allis's nerve " c " (see text). Distributed to 



tissues behind and below eye. 



11. Hyomandibular sensory canal, showing sense 



organ 8 of this line. 



12. External mandibular lateral line nerve. 



13. Mandibular pit organ. 



14. Optic chiasma. 



15. Posterior extremity of cerebral hemispheres 



(no lateral ventricles). 

 1(5. Frontal bone. 



