1. ANATOMY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
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( Schnitzlein, 1964; Nieuwenhuys, 196% ) . In the gar, Lepisosteus osseus,
the bulb can be many centimeters from the olfactory integrating centers
found within the piriform area of the telencephalon. In other species
such as sharks, Scylliorhinus, the two bulbs lie lateral to the telencephalic
hemispheres.
In most fish, the mitral cells are arranged in a diffuse layer which lies
immediately central to the glomerula zone of the nasal cavity. However,
mitral cells can be found to occupy more peripheral positions within
the bulb and often are scattered along the glomerulus in lampreys
( Nieuwenhuys, 1967b). With few exceptions intcqlomerula association
cells have been demonstrated for selachians, actinopterygians, and dipnonns. Within the olfactory bulb there are granular elements which form
the periventricular bulbar layer of gray matter. This layer of gray matter
is extensive, and its neurons provide distinct axons which contribute to
the olfactory tract. Dendrites of the cells within the gray matter comprise a significant portion of the glomerulus. Within the deep granular
layer of the glomerulus some neurons possess short axons that innervate
other glomerular neurons. Thus, not all the granular cells send axons
into the olfactory tract.
The olfactory bulbs are joined by an interbulbar comniissure located
in the brain proper. Efferent nerve fibers from the olfactory bulb have
becm located in the anterior commissure, habenular commissure, and
other areas ( Nieuwenhuys, 1967b ) . These anatomical observations have
been corroborated by electrophysiological data which have indicated
that the central interbulbar coniniissures are part of the neural pathway
for the integration of olfactory information.
B. Telencephalic Anatomy
The anatomy of the telencephalon of fish has presented certain
unique problems for neuroanatomists because structures from which
homologies are drawn in higher vertebrates appear to be lacking in the
fish telencephalon. For instance, there is the lack of a demonstrable
lateral ventricle, the lack of a prominent ventricular sulcus, and the
presence of an extensive and thin roof plate. For these reasons it is
difficult to establish homology bctwecm comparable regions of the fish
telencc>phalon and the tc,lencephnlon of other vertcbratcs ( Droogleever
Fortuyn, 1961; Nieuwenhuys, 1962a,b, 1967b; Schnitzlein, 1964 ) . The
telencephalon of bony fishes as in other vertebrates has its embryonic
origin in a tubc-shaped structure ( Nicwwenhuys, 1959, 1960, 1962a-d,
1963, 1967b). As the telencephalon develops there appears to be only
11
( Schnitzlein, 1964; Nieuwenhuys, 196% ) . In the gar, Lepisosteus osseus,
the bulb can be many centimeters from the olfactory integrating centers
found within the piriform area of the telencephalon. In other species
such as sharks, Scylliorhinus, the two bulbs lie lateral to the telencephalic
hemispheres.
In most fish, the mitral cells are arranged in a diffuse layer which lies
immediately central to the glomerula zone of the nasal cavity. However,
mitral cells can be found to occupy more peripheral positions within
the bulb and often are scattered along the glomerulus in lampreys
( Nieuwenhuys, 1967b). With few exceptions intcqlomerula association
cells have been demonstrated for selachians, actinopterygians, and dipnonns. Within the olfactory bulb there are granular elements which form
the periventricular bulbar layer of gray matter. This layer of gray matter
is extensive, and its neurons provide distinct axons which contribute to
the olfactory tract. Dendrites of the cells within the gray matter comprise a significant portion of the glomerulus. Within the deep granular
layer of the glomerulus some neurons possess short axons that innervate
other glomerular neurons. Thus, not all the granular cells send axons
into the olfactory tract.
The olfactory bulbs are joined by an interbulbar comniissure located
in the brain proper. Efferent nerve fibers from the olfactory bulb have
becm located in the anterior commissure, habenular commissure, and
other areas ( Nieuwenhuys, 1967b ) . These anatomical observations have
been corroborated by electrophysiological data which have indicated
that the central interbulbar coniniissures are part of the neural pathway
for the integration of olfactory information.
B. Telencephalic Anatomy
The anatomy of the telencephalon of fish has presented certain
unique problems for neuroanatomists because structures from which
homologies are drawn in higher vertebrates appear to be lacking in the
fish telencephalon. For instance, there is the lack of a demonstrable
lateral ventricle, the lack of a prominent ventricular sulcus, and the
presence of an extensive and thin roof plate. For these reasons it is
difficult to establish homology bctwecm comparable regions of the fish
telencc>phalon and the tc,lencephnlon of other vertcbratcs ( Droogleever
Fortuyn, 1961; Nieuwenhuys, 1962a,b, 1967b; Schnitzlein, 1964 ) . The
telencephalon of bony fishes as in other vertebrates has its embryonic
origin in a tubc-shaped structure ( Nicwwenhuys, 1959, 1960, 1962a-d,
1963, 1967b). As the telencephalon develops there appears to be only