LATERAL LINE SYSTEM IN EXTINCT AMPHIBIA SBA 
that, even among the siluroids, the supraorbital and infraorbital canals 
may separate either in the frontal or in the post-frontal, and still more 
clearly by the presence of a canal and a sense organ in the inter-oper- 
culum, as well as the preoperculum. * * * * Moreover in cases 
where the dermal skeleton is greatly reduced, while the sensory organs 
of the lateral line system do not suffer a corresponding reduction, as 
in Lophius, the canals disappear and the courses of the lateral lines, as 
indicated by the rows of naked sense organs, cease to be dependent upon 
the positions of the underlying bones.” And further he remarks: 
“Tt should be noted, however, that all lateral line ossicles are dermal 
bones specialized for this purpose, and that the canals do not penetrate 
the bones belonging to the primordial cranium. * * * * (Herrick, 
10 p. 259). 
The value of these observations upon any attempted correla- 
tion of the cranial elements of the fishes and Amphibia, such as 
has been attempted by several authors, is at once evident. If 
the lateral line canals control the developing cranial elements, 
any correlation which does not take into consideration the lateral 
line system is superficial. In an attempt at correlating the ele- 
ments of the temporal region, the writer has already (’08) re- 
ferred to the importance of the relation of the lateral line canals 
of the head and the cranial elements. The bones of the skull of 
the ancient Amphibia are all dermal and lay upon the primordial 
chondrocranium, with the possible exception of the bones bound- 
ing the brain case, and even these seem largely cartilaginous. 
Broom remarks” that the inner ear of the labyrinthodonts was 
contained in cartilage. 
It is certain, that there is a high degree of similarity in arrange- 
ment in the peripheral osseous elements of fishes and amphib- 
ians. Whether the lateral line canals are the primary or second- 
ary element is a matter that will have to be experimentally 
determined. It is an interesting fact, however, that in the more 
mature phyla the osseous elements retain their relative position, 
in the absence of the lateral line canals; but canals are only want- 
ing in the higher and more specialized forms after the osseous 
elements may have become fixed by the lateral line canals, and 
after the sense organs have disappeared from the grooves inthe 
* Bull. Amer. Museum Natl. History, vol. 32, art. 38, p. 574, 1913. 
