57 
opisthotic, which is thus undoubtedly the bone miscalled in his text 
the petrosal. In Amia this same nerve pierces the intercalar, to reach 
and supply a lateral organ in the squamosal and the pit organs of 
the middle head line of my descriptions, while in Scomber its prob- 
able homologue, the nerve already referred to that has its appar- 
ent origin from the first vagus nerve, runs upward and mesially, 
postero-ventral to the hind end of the intercalar, to supply a lateral 
organ in the squamosal. In Polypterus the vagus foramen lies be- 
tween the so-called opisthotic and occipital bones. In Amia it lies 
between the intercalar and the occipitale laterale, almost completely 
enclosed in the anterior edge of the latter bone, in which it is enti- 
rely enclosed in Scomber. 
In Alepocephalus rostratus, so far as can be judged from GEGEN- 
BAUR’S descriptions and figures (No. 17), the primary and secondary 
components of the squamosal, if they both exist, must be entirely 
separate and distinct from each other, as they are in Polypterus, and 
there is apparently no fibrous component. The bone is said to 
enclose the summit of the external semicircular canal; and between 
that part of the bone that is formed on the external surface of the 
cartilage and the thin layer that lines its inner surface and directly 
encloses the space traversed by the semicircular canal, there is a thin 
persistent layer of cartilage. The bone thus represents a stage of 
development similar to that described by Scumrp-Monnarp in the 
young of Esox, excepting that no indication whatever is given of a 
lateral canal in any way related to it. The shape, alone, of the bone, 
as shown in the figures, seems to preclude the possibility of its being 
traversed by such a canal, and yet no separate canal element can be 
recognised in the descriptions, unless it be described in the bone of 
which GEGENBAUR says: “Ein einzelnes kleines Knochenstückchen ist 
endlich noch vom Schädeldach zu erwähnen, wo es auf dem Parietale 
und dem Occipitale externum aufliegt. Es gehört gleichfalls dem 
Hautröhrensysteme an und trägt die Mündungen von 2—3 Röhrchen.” 
This little bone would seem, however, from its position, to be an 
extrascapular. If it be such, and if the squamosal is not traversed 
by a canal, then either the otic and more posterior portions of the 
main infraorbital canal of Alepocephalus must be entirely wanting, 
must be represented, in part, in that highly developed posterior exten- 
sion of the supraorbital canal that is shown in the frontal bone, or 
they must be, as often happens for certain portions of the sensory 
system, enclosed in thin bony tubes or scales attached to the integ- 
ument, and so easily removed unnoticed. This latter supposition 
