from the branch to organ 4 after th e main branch had entered the main infraorbital canal itself,
and then continued its course inside th a t canal. This all certainly indicates th a t organs 4 and 5 lie
so close together a t the time th a t they become enclosed in the canal th a t no primary tube can be
developed between them, this tube thus never being formed. In Menidia also these two organs lie
close together (Herrick, ’99, p. 198), b u t there is a primary tube between them as there is in Cottus.
In Gadus (Cole ’98) there is, as in Scorpaena, no primary tube between th e 4 th. and 5 th. organs
of th e supraorbital canal, b u t Gadus differs from Scorpaena in th a t there is no 6 th. supraorbital
organ and related primary tube.
Organ 6 of Scorpaena differs from th e other organs of th e line in being much smaller th an
any of them. I t is innervated b y th e first b ranch of the ophthalmicus lateralis, this branch perforating
th e alisphenoid from its lateral surface and then running upward inside th e cranial cavity to perforate
th e frontal immediately beneath th e organ it supplies.
The preoperculo-mandibular canal begins near th e symphysis of th e mandible, and, running
posteriorly, traverses th e dentary, articular and preopercular, and th en anastomoses with the main
infraorbital canal a t th e hind end of th e squamosal. The canal lodges eleven sense organs, four lying
in th e dentary, one in th e articular and six in the preopercular, all of them innervated by branches
of th e ramus mandibularis externus facialis. A primary tube arises from the canal between each
two consecutive organs, this making, with th e two terminal tubes, twelve tubes in all. The eleventh
tubé anastomoses secondarily, as already stated, with the seventh tube of the main infraorbital canal,
th e twelfth tube anastomosing primarily with the te n th infraorbital tube and secondarily with the
eighth and eleventh tubes of th e same line.
6. N E R V E S .
The investigation of the nervous system of th e several fishes of th e group has been mainly
limited to th e ad u lt of Scorpaena scrofa, and to serial sections of small specimens of th a t fish and of
Lepidotrigla aspera; b u t certain features of the innervation in the adults of C ottus octodecimospinosus
and Trigla hirundo, in small specimens of Dactylopterus volitans, and in embryos of Cottus scorpius
have been also somewhat carefully examined. The intention a t first was to simply determine the
relations of the roots, ganglia and proximal portions of th e cranial nerves to th e skeletal elements,
th e study of the skeleton being th e principal object of th e research; b u t as certain of the series of
sections examined permitted th e tracing, with comparative accuracy, of th e components of the
several nerves, these results, so far as obtained, are given. There was however no a ttem p t whatever
to make thèse results complete. So far as given they are intended to be correct.
In recent English and American works on th e cranial nerves of the lower vertebrates there
is a marked tendency to consider th e central origin of a given cranial nerve of much more importance
for th e determination of its segmental position th a n th e course of th e nerve and its general
relations to the skeletal elements. Underlying this manner of considering th e subject, is the implied
acceptance of the neurone theory of the nervous, system, according to which theory all nerve fibers
grow either centrifugally or centripetally between two primarily disconnected points, choosing always
the p a th of least resistance. Directly opposed to this manner of considering th e subject is th e earlier
conception of the nervous system, recently re-presented by Gaskel (’05), according to which th e peripheral
and central cells are from the very beginning, and as soon as they begin their separate exis-
B 77 ~
tence, always connected by nervous tissue. While m y own work has never yet led me to investigate,
or even to seriously Consider, the manner in which the cranial nerves, develop, it has led me to conclude,
as I have already had occasion to state, that; (I) the relations of the nerves to the skeletal
elements are so remarkably constant th a t if the nerve itself does not exist from the very beginn in g ,
some tissue or condition of tissue, defining its p a th , or some markedly strong inherited tendency
must certainly so exist; and (2), that whenever a nerve is deflected from its accustomed and apparently
predetermined path, careful examination and consideration will almost always show that it has
simply been pushed or pulled one way or the other, surrounded to a different extent or in a different
manner by the encroaching and enveloping growth of adjacent- tissues, or even actually displaced
relative to certain tissues or structures by a variation in the relative time, or in the relative degree
of development of the nerve and those other tissues. That there are certain apparently inexplicable
exceptions to this rule, I know full well.
According to the latter of these two conceptions of the nervous system, the general course
of a nerve and its relations to the skeletal and other elements, properly determined, definitely define
the segmental position of the nerve, and its centers of origin must be in accord with those determinations.
According to the other conception, carried to its legitimate extreme, the course of nerve fibers
is not necessarily segmental, and, the terminal distribution of sensory fibers also not being necessarily
segmental, the only positive criterion of the segment or segments to which the component
fibers of a certain nerve belong is their points of origin in the central nervous system. Furthermore,
the cranial segment to which it is assumed th a t certain fibers must necessarily belong having been
determined by their central origin, the elements of accident, individual experience, or even a sort
of elective selection are introduced as natural and constant occurrences to explain the apparently
unsegmental peripheral course of certain of those fibers; and where certain sensory fibers are assumed,
in the wording of the descriptions, to grow centripetally from certain sense organs to the brain,
the same elements of accident, experience or elective selection may determine their peripheral
course in one segment and their central origin in another. I t is needless to refer to the many
expressions and statements that seem to lead legitimately to these conclusions, and while these
statements definitely impress the reader it is possible that they may not always give correctly
the definite opinions of the authors making them.
These two radically different conceptions of the origin and development of the peripheral nervous
system lead, frequently, to totally different interpretations of the facts of distribution, this being especially
marked in relation to the branches of the trigemino-facialis complex. Stannius, apparently an advocate
of the earlier conception of the nervous system, assigned the fibers of this complex to the trigeminus
or facialis nerves according as they issued from the skiill by one set of foramina or another, or had a
distribution to what he considered as trigeminus or facialis regions; and he accordingly considered the
roots of the complex as partly trigeminus, partly facialis, and partly mixed. Later authors first assigned
all the lateralis fibers of the complex to the facialis, irrespective of their course and distribution, and
now, still later, recent advocates of the component theory assign all the communis fibers also to that
same nerve. I, myself, have accepted and advocated the assigning of the lateralis fibers of the complex
to the facialis, but as I am not prepared to accept the assigning of the communis fibers to th a t nerve,
I begin to doubt the justice of so assigning the lateralis ones, This will be further discussed when
describing certain of the branches of the complex. To avoid confusion I still adhere to the nomen