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



system on tlie morjiliology of the skull *. This author discovered the important fact 

 that the frontal bone, for example, consisted of two parts — the frontal projierly so-called 

 + a fused lateral line ossicle. The supra-orbital canal in the region of the frontal first 

 acquired its bony support corresponding to a true lateral line ossicle, and the latter, as 

 development proceeded, became fused on to the frontal. The same process was observed 

 in the case of the sphenotic, pterotic, dentary, and articular. In the Cod this process 

 may be easily deduced from the structure of the articular portion of the hyomandibular 

 canal. We may therefore classify the osseous support of the lateral line in the Cod and 

 perhaps other forms as follows : — 



Lateral line Ossicles. True Cranial Bones + fused Lateral line Ossicles. 



Nasal. 



Lachrymal or adnasal. Frontal. 



Supra- or infra- (with post-) orbitals. Sphenotic (most forms). 



Dermal Sphenotic {Amia)= the Post-frontal. Pterotic (most forms). 



Dermal Pterotic {Gadiis) —the Squamosal. Dentary. 



Supra-temporals. Articular. 

 Pre-operculum. 



Two things must be pointed out with reference to this tabic: first, I fully agree with 

 McMurrich that the nasal and pre-operculumi are true lateral line ossicles ; second, there 

 is some doubt in the Cod as to the nature of the pterotic. In Amiurus there is no doubt 

 that it is a cranial bone bearing a fused lateral line ossicle. In Gadus, however, the 

 bone usually termed the pterotic has no connection with the ear, and may be easily 

 detached from the underlying ear bones. It seems probable, therefore, that the Cod's 

 "pterotic" is a lateral line ossicle which has not become fused on to the adjacent true 

 pterotic (cp. particularly p. 181) t- 



Whilst it is obvious from these facts that the lateral line system has no connection 

 whatever with the primitive cartilaginous and membrane skull, such is by no means the 

 case with regard to the later development of the latter. Whilst, further, alcove the 

 Amphibia, the lateral canal system and its nerves completely disappear, leaving no traces 

 behind (omitting the auditory organ), we cannot say the same in the matter of the bony 

 supports of the canals. The nasal, for example, performs a doiible function — on the one 

 hand supporting a portion of the supra-orbital canal, for which purpose it was primarily 

 developed ; on the other hand, having relations with the nasal capsule, which represents 

 a. secondary modification. When, therefore, the supra-orbital canal disappeared, the 

 nasal would remain behind, to perform its accessory nasal function. It therefore seems 

 to me certain that the higher vertebrate skull bears very considerable traces of the 

 lateral line system of Fishes and Amphibians and it would be a very interesting study 

 to determine what these relations are. For example, admitting the homology between 

 the ear and the lateral line system, to what extent are the bones of the auditory capsule 

 profoundly modified lateral line ossicles ? 



* MoMurr'.ch, by tho way, ulso considers the lachrymal to be the luodified first sub-orbital. So a'so does Pollard, 

 I,s02(i6o, p. 410). 



t See Postscript, p. 20o. 



