A Guide to the Study of Fishes, Volume 1 (of 2)

r vertebrates, the nerve substance is divided into gray matter and white matter, or nerve-cells and nerve-fibres. In the fish, however, the whole nervous system is relatively small, and the

the space between the dura mater, which lines the skull-cavity, and the arachnoid membra

en from above the brain of a typical fish seems to consist of five lobes, four of them in pairs, the fifth posterior to these and placed on the median line. The posteri

lobes of the cerebrum, also called the hemispheres, or prosencephalon. These lobes are usually smaller than the optic lobes and solid. In some fishes they are crossed by a furrow, but are never corrugated as in the b

hark (Squatina squati

anial nerve

cephalon

piph

lamenc

nd crani

th crani

h crani

nth crani

rth ven

phalon (op

cephalon

phalon (ce

im?ra monstrosa. (Af

pterus annectens. (Afte

m are very small. In the sharks and rays the large cerebral hemispheres are usually coalescent into one, and the olfactory nerves dilate into large ganglia below the nostrils. The optic lobes are smaller than the hemispheres and also coalescent. The cerebellum

higher vertebrates. In some of the lizards this epiphysis is largely developed, bearing at its tip a rudimentary eye. This leaves no doubt that in these forms it has an optic f

Perch, Perca flave

actory

um (prose

piph

obes (mese

llum (epen

oblongata (m

t crani

nd crani

th crani

h crani

nth crani

hth crani

h crania

h crani

or (Dekay). Head of Lake Lamprey,

rved in reptiles as "an outcome of the life-habit which concealed the animal in sand or mud, and allowed the forehead surface alone to protrude, the median eye thus

a median eye in lizards was a modification of a secondary character. On consideration of the evidence, Dr. Dean concludes that "the pineal structures of the true fishes do not tend to confirm the theory that the epiphysis of the ancestral vertebrates was connected with a median unpaired eye. It would appear, on the other hand, that both in their rece

still uncertain. The different ganglia are all solid and are placed in pairs. It is thought that the cerebellum is wanting in these fishes, or repr

e of brain, the band-like spinal

astic. In a few fishes (headfish, trunkfish) in which the posterior part of the body is shortened or degenerate, the spinal cord is much shortened, and replaced behind by a structure called cauda equina

with those of the higher animals. They are, however, fewer in number, both la

The optic nerves, or second pair, extend from the eye to the base of the optic lobes. In Cyclostomes these nerves run from each eye to the lobe of its own side. In the bony fishes, or

th pair, nervus trigeminus, and the seventh pair, nervus facialis, arise from the medulla oblongata and are very close together. Their various branches, sensory and motor, rami

astric nerve, arises from strong roots in the corpus restiforme and the lower part of the medulla oblongata. Its nerves, motor and sensory, reach the muscles of the gill-cavity, heart, stomach, and air-bladder, as well as t

in higher vertebrates. The anterior root of each nerve is without ganglionic enlargement and contains only mot

rates is found in all the Teleostei, or bony fishes, and in the

TNO

name given to the region of the optic thalami, b

ecent and Fo