HERRICK, (Verves of Silurotd Fishes. 239 
of slight value either to taxonomy or to phylogeny. It should 
be noted, however, that all lateral line ossicles are dermal bones 
specalized for this purpose, and that the canals do not penetrate 
bones belonging to the primordial cranium, though some recent 
descriptions have stated this to occur in Ameiurus. 
6. The bone of Menidia which I termed the extra- 
scapular in my contribution published in 1899 is probably a 
fusion of the extra-scapular and the post-temporal, since the 
extra-scapular, as defined by Allis, is a dermal ossification (or 
several such) developed to carry the supra-temporal commissure 
of the lateral line canal, while the post-temporal belongs to the 
shoulder girdle. 
7. The composition and distribution of the several nerves 
need not be reviewed in detail here. The most striking feature 
is the fusion in many of the cutaneous nerves even to their 
minute ramifications of two or three of the components, so 
that their analysis is a matter of extreme difficulty, especially 
as the components do not differ in the caliber of their fibers so 
much as in most other fishes. Nevertheless this analysis can 
be effected in the majority of cases and in the hundreds of 
sense organs whose innervation has been accurately determined 
no exception has been found to the laws of nerve supply laid 
down above. 
8. Ther. mandibularis internus of the facialis appears to 
be lacking in Ameiurus; for, though the hyomandibular trunk 
receives some communis fibers, these apparently all distribute 
to terminal buds of the outer skin of the opercular region and 
none are continued inward to supply the mucous lining of the 
mouth. 
g. Ther. mandibularis externus facialis divides into two 
portions, an internal one for the mandibular lateral line canal 
organs, and an outer one, which I have termed the cutaneous 
branch, for pit organs of both the large and the small variety 
along the course of this canal. The latter nerve carries both 
communis and general cutaneous fibers in addition to its proper 
lateralis fibers. Some writers on siluroid nerves have erroniously 
called this cutaneous branch the main r. mandibularis externus, 
