Inferior vestibular nucleus – This nucleus begins caudally in the
*medulla near the *external cuneate nucleus and extends
rostrally along the medial border of the *inferior cerebel-
lar peduncle. Its neurons receive afferents from the ves-
tibular ganglion and their efferents target the *nodulus and
the *flocculus. Some axons also join the *medial longitu-
dinal fasciculus and terminate in cranial motor nuclei (III,
IV, VI) that control extraocular muscles.Infundibular recess – Small recess of the third ventricle that evagi-
nates into the *infundibulum.
Infundibulum – Stalk extending from the mediobasal *hypothala-
mus that contains the median eminence and forms a link to
the pituitary gland.Insula (insular cortex) – Large buried neocortical region behind the
lateral fissure. Its components (gyri breves, gyri longus)
are continuous internally with the *frontal, *parietal and
*temporal lobes.Intercalated cell groups (amygdala) – Densely packed clusters of
small cells that are typically embedded in the white matter
between nuclei in the basolateral and corticomedial com-
plexes in the *amygdala.Interhemispheric fissure – Longitudinal cleft that separates the
two cerebral hemispheres. It is traversed by the *corpus
callosum.Internal capsule – Massive fiber tract between the *thalamus and
*striatum, composed of thalamocortical and corticofugal
fibers. It is continuous with the *corona radiata rostrally,
and the *cerebral peduncle caudally.Interpeduncular nucleus – Midline mesencephalic structure above
the interpeduncular fossa and between the *cerebral pedun-
cles. It is the target of fibers of the *habenulo-interpedun-
cular tract.Interpositus nucleus (cerebellum) – A deep cerebellar nucleus
located between the *dentate nucleus and the *fastigial
nucleus. It contains a lateral and a medial group of neu-
rons, the emboliform near the *dentate nucleus, and the
globosus near the *fastigial nucleus.Islands of Calleja – Scattered clusters of small granule cells within
the *olfactory tubercle and along the medial border of the
*nucleus accumbens.Isthmal glioepithelium/ependyma – The putative source of glia
and the site of proliferating ependymal cells in the *isth-
mus that lines the posterior *aqueduct. This structure
replaces the isthmal neuroepithelium.Isthmus – Interconnecting bridge between the *midbrain and the
*pons that is more prominent during earlier brain develop-
ment than in the third trimester.L
Lamina terminalis – Anterior membranous border of the *third
ventricle. It is the site where the anterior neuropore closes
during early embryonic development.Lateral corticospinal tract – A component of the larger *corticofu-
gal tract that originates mainly from layer V in the motor
area (including the large Betz pyramidal cells) and other
areas of the cerebral cortex that controls skeletal muscles in
the contralateral trunk and limbs. Axons carrying somatic
motor output cross the midline in the *pyramidal decussa-
tion and descend through the entire length of the spinal cord
in the dorsolateral part of the *lateral funiculus. Axons
leave the tract in a topographically organized manner to
terminate directly on spinal motoneurons in the ventral
horn from cervical to sacral levels.Lateral fissure – Deep, oblique sulcus (also known as the Sylvian
fissure) that separates the *frontal lobe and the *paracentral
lobule anterodorsally from the *temporal lobe ventrally.Lateral funiculus (spinal cord) – Region of the spinal cord white
matter that flanks the gray matter laterally. Major com-
ponents of the lateral funiculus are the *lateral corticospi-
nal tract, the *spinocephalic tract, and the *spinocerebellar
tracts.Lateral geniculate body – Distinct thalamic region composed of
the laminated dorsal lateral geniculate nucleus and its fiber
capsule. The principal afferents of this visual relay struc-
ture are ipsi- and contralateral fibers of the *optic tract;
the principal target of its efferents is the ipsilateral *striate
cortex. The connections of the lateral geniculate nucleus
and the striate cortex are reciprocal.Lateral hypothalamic area – An ill-defined fibrous region of the
*hypothalamus with scattered neurons medial to the cere-
bral peduncle. It is traversed by many fiber tracts, includ-
ing the *medial forebrain bundle. The region has been
implicated in behavioral arousal and motivation.Lateral lemniscus – The fiber tract on the lateral surface of the
*pons that contains secondary auditory fibers from the
dorsal and ventral *cochlear nuclei and higher-order audi-
tory fibers from the *superior olivary complex. The dorsal
and ventral *nuclei of the lateral lemniscus are embedded
within the fiber tract.Lateral migratory stream (cortical) – Tangentially-migrating neu-
rons and glia in the developing *cerebral cortex that
leave dorsal parts of the neocortical *neuroepithelium and
migrate laterally and ventrally to insular and temporal cor-
tical areas and other telencephalic structures that lack a
nearby germinal matrix. The bulk of the lateral migratory
stream follows a trajectory outlined by the receding *sub-
ventricular zone between the *basal ganglia and the lateral
cortex.Lateral nucleus (amygdala) – The most lateral nucleus in the
*basolateral complex of the *amygdala. Cells from the
*lateral migratory stream appear to enter the nucleus at
the distinctive saw-toothed lateral edge. This nucleus is a
major recipient of cortical input from the *temporal lobe,
*occipital lobe, *insular gyrus, and *orbital gyrus. It also
gets input from the *posterior complex of the thalamus.
It projects to the *entorhinal cortex, *temporal cortex,
*orbital cortex, *insular cortex, *nucleus accumbens, and*dorsomedial thalamic nucleus.
Lateral preoptic area – An anterior continuation of the lateral
hypothalamic area in the *preoptic area.Lateral reticular nucleus – A relatively discrete group of neurons
in the caudal medulla, dorsolateral to the *inferior olive.
The neurons of this precerebellar relay nucleus receive top-
ographic exteroceptive and proprioceptive afferents from
the *spinocephalic tract and project ipsilaterally to the
*cerebellum via the *inferior cerebellar peduncle.Lateral septal nucleus – An indistinct gray mass in the lateral
*septum that is closely associated with the *fornix, which
provides input to these neurons.Lateral tuberal nucleus (hypothalamus) – Two or three distinct
spherical masses near the inferior surface of the *lateral
hypothalamic area. These neurons may play a role in ther-
moregulation and food intake.Lateral ventricles – Paired cavities of the ventricular system in the
telencephalon. They are connected with the *third ventri-
cle in the diencephalon by the *foramen of Monro.An asterisk in front of a term indicates that it has a separate entry in the Glossary with additional
information. Terms referring to transient developmental structures are underlined.
GLOSSARY