The Human Brain During the Third Trimester

guishable parts, the *gracile fasciculus medially, and the

*cuneate fasciculus laterally.

Dorsomedial nucleus (hypothalamus) – Area situated above the

more distinct *ventromedial nucleus of the hypothalamus.

Its principal connections are with the *bed nucleus of the

stria terminalis and the *septum.

Dorsomedial nucleus (thalamus) – Also known as the medial

dorsal nucleus, this component of the *dorsal complex is

situated between the internal medullary lamina and the

periventricular gray, and has a large-celled and small-celled

division. Its principal connections are with the *amyg-

dala, the *hypothalamus, the *olfactory tubercle, and the

*orbital gyrus. It is considered a paleothalamic compo-

nent of the limbic system rather than as a neothalamic relay

nucleus to the neocortex.

E

Endopiriform nucleus – Small telencephalic nucleus deep to

the *primary olfactory cortex and ventral to the *claus-

trum. The *lateral migratory stream percolates through

this nucleus.

Entorhinal cortex – Multilayered cortical component of the *para-

hippocampal gyrus. It is bordered internally by the *subic-

ular complex and is separated from the *neocortex by the

rhinal sulcus. It is the source of the perforant pathway to

the *hippocampus.

Ependyma – Layer of cuboidal cells that line the lumen of the per-

manent brain *ventricles and *central canal after dissolu-

tion of the proliferative *neuroepithelium.

External capsule – Slender fiber band situated between the *claus-

trum and the *putamen.

External cuneate nucleus – Situated lateral to the *cuneate nucleus

in the *medulla, also known as the accessory cuneate

nucleus, it is the source of the cuneocerebellar tract. The

nucleus relays somesthetic and proprioceptive information

from anterior regions of the body to the *cerebellum.

External germinal layer (cerebellum) – Subpial, secondary germi-

nal matrix of the cerebellar cortex, the source of its gran-

ule, stellate, and basket cells. It has two components, an

outer proliferative zone and an inner premigratory zone.

It persists as a source of neurons over the surface of the

human cerebellar cortex until the end of the second year of

postnatal life.

F

Facial motor nucleus – A large aggregate of somatic motor neurons

in the ventrolateral pons dorsal to the *superior olive com-

plex. It is the source of the motor fibers of *nerve VII that

innervate the facial mimetic muscles. Subdivisions of this

nucleus innervate different facial muscles.

Fasciola cinereum – Transitional region that wraps around the sple-

nium of the *corpus callosum connecting a primordium

of the hippocampal *dentate gyrus to the *induseum gri-

seum.

Fastigial nucleus (cerebellum) – A deep nucleus of the *cerebel-

lum, also known as the medial cerebellar nucleus. It is the

target of Purkinje cell axons that originate in the *vermis.

Its axons contribute to the large efferent system that leaves

the cerebellum.

Fimbria – Large fiber tract of the *hippocampus that runs parallel

with and then joins the *fornix.

Floccular peduncle – Stalk in the cerebellum that connects the

*flocculus with the *nodulus. The *germinal trigone is

often strung out along the base of this peduncle.

Flocculus (cerebellum) – Lateral extension of the vermal *nodulus

in the *cerebellar hemisphere. The principal connections

of the two, sometimes called the flocculonodular lobe, are

with the vestibular system.

Folium (cerebellum VIIa) – Component of the *central lobe, ante-

rior to the *tuber. The hemispheric extension of the folium

is *crus I of the ansiform lobule. Together with the *tuber,

this is a late-maturing region of the cerebellar cortex.

Foramen of Monro – Paired channels in the ventricular system that

connect the *lateral ventricles in the telencephalon with the

*third ventricle in the diencephalon.

Forel’s fields – Subthalamic tegmental field (H

1

and H

2

) with fiber

bundles of the *ansa lenticularis, lenticular fasciculus, and

subthalamic fasciculus.

Fornical glioepithelium – Germinal matrix lining the fornix that

persists for some time after the dissolution of the hippo-

campal neuroepithelium. It is the putative germinal source

of the oligodendrocytes of the fornix.

Fornix – The principal efferent fiber tract of the *hippocampus.

The body of the fornix courses forward under the *corpus

callosum and above the *thalamus, then turns downward

and subdivides into a precommissural part that distributes

fibers to the *septum, and a postcommissural part that

curves behind the *anterior commissure. The postcommis-

sural fibers traverse the diencephalon and most of them ter-

minate in the nuclei of the thalamic *anterior complex and

the *mammillary body.

Fourth ventricle – Region of the ventricular system in the *pons

and *medulla between the *aqueduct rostrally and the

*central canal caudally.

Fourth ventricle (embryonic) – The neuroepithelium surrounding

the hypertrophied fourth ventricle and its several recesses

is the source of neurons and glia of the *medulla, the *pons

and the *cerebellum. Many of the neurons migrate over

long distances to their settling sites.

Frontal lobe – Region of the cerebral cortex anterior to the *central

sulcus. Some components of this region, e.g., *precentral

gyrus and *orbital gyrus, are often excluded. Its major con-

volutions are the superior, middle and inferior frontal gyri.

Minor convolutions are the gyrus rectus, the inferior rostral

gyrus, and the superior rostral gyrus.

Frontal neuroepithelium – Putative source of the neurons and glia

of the *frontal lobe. Before settling in the cortical plate, its

cells form the frontal *subventricular zone and *stratified

transitional field.

G

Germinal trigone (cerebellum) – Proliferative germinal matrix in

the fourth ventricle beneath the *nodulus that contains three

prongs: the *cerebellar neuroepithelium/glioepithelium, the

*choroid plexus, and the *external germinal layer.

Glial sling (corpus callosum) – See Callosal sling.

Glioepithelium – Fate-restricted germinal matrix in the developing

brain, the presumed source of neuroglia (astrocytes and oli-

godendroglia). Glioepithelia are easiest to recognize with-

out special glial markers at sites of considerable distance

from neuronal aggregates or their migratory routes, such

as along the *corpus callosum, the *fornix, and the *stria

terminalis.

Globus pallidus – Component of the *striatum, situated medial

to the *putamen, with an external (lateral) and internal

(medial) segment. Pallidal fibers are the principal efferents

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