The pia mater is the only listed structure that is derived from cranial neural crest cells. For a
summary of germ cell derivatives refer to Table 4.1.

The roof plate and its pial covering give rise to the choroid plexus, which invaginates into
the fourth ventricle. The alar plate gives rise to sensory neurons; the basal plate gives rise to
motor neurons; the floor plate contains decussating fibers; the rhombic lips give rise to the
cerebellum

The pontine flexure develops between the metencephalon (pons) and the myelencephalon
(medulla). The pontine flexure results in lateral expansion of the walls of the metencephalon
and myelencephalon, stretching of the roof of the fourth ventricle, and widening of the floor of
the fourth ventricle (rhomboid fossa).

The globus pallidus has its origin from the diencephalon. Neuroblasts from the subthalamus
migrate into the telencephalic white matter to form the globus pallidus.

New evidence documents that the external granular layer gives rise only to the granule cells
of the internal granular layer and not to the basket (inner stellate) or stellate (outer stellate)
neurons, as was long thought. The giant cells of Betz are found in the cerebral cortex.

Myelinated preganglionic sympathetic neurons have their cell bodies in the intermediolateral cell column of the lateral horn; this cell column extends from C8 to L1. Myelinated
preganglionic parasympathetic neurons have their cell bodies in the sacral autonomic nucleus,
from S2 to S4.

Arnold-Chiari syndrome is a cerebellomedullary malformation in which the caudal vermis
and medulla herniate through the foramen magnum, resulting in communicating hydrocephalus. Arnold-Chiari syndrome is frequently associated with spina bifida

Tanycytes are modified ependymal cells, found principally in the third ventricle. Tanycytes
transport substances from the CSF to the hypophyseal portal system.

The sulcus limitans separates the sensory alar from the motor basal plates. It is found in the
developing spinal cord and on the surface of the adult rhomboid fossa of the fourth ventricle.
The bulbopontine sulcus (inferior pontine sulcus) separates the medulla from the pons.
The hypothalamic sulcus separates the thalamus from the hypothalamus. The rhinal sulcus
separates the neocortex from the allocortex.

At birth, the conus medullaris extends to L3, and in the adult it extends to the L1–L2 interspace. At 8 weeks, the spinal cord extends the entire length of the vertebral canal.

The most common cause of congenital hydrocephalus is aqueductal stenosis.

Axons of the corticospinal tracts are fully myelinated by the end of the second postnatal year;
Babinski sign (extensor plantar reflex) is usually not elicitable before myelination of the corticospinal tracts.

Cranium bifidum with meningoencephalocele consists of the herniation of meninges and
brain tissue through a defect in occipital bone.

Failure of the anterior neuropore to close results in anencephaly. The brain fails to develop;
no cranial vault is formed.

The superior salivatory nucleus represents the general visceral efferent (GVE) column of the
pons. All somatic and visceral motor nuclei are derived from the basal plate. The cerebellum
and pontine nuclei and the sensory nuclei of cranial nerves are derivatives of the alar plate

Hydranencephaly consists of huge intracerebral cavitation resulting from infarction in the
territory of the internal carotid artery

The abducent nucleus represents the general somatic efferent (GSE) column of the pons

The hippocampus develops from the telencephalon. The pineal gland, hypothalamus, CN II,
and the globus pallidus are derived from the diencephalon.

The anterior and posterior neuropores close during week 4 of development—the anterior
on day 25, the posterior on day 27. Failure of the anterior neuropore to close results in
anencephaly; failure of the posterior neuropore to close results in myeloschisis.

The neurohypophysis develops from the diencephalon. The adenohypophysis (pars distalis,
pars tuberalis, and pars intermedia) develops from Rathke pouch, an ectodermal diverticulum
of the stomodeum. The caudate nucleus and olfactory bulbs develop from the telencephalon.
The cerebellum develops from the metencephalon.

Dandy-Walker syndrome is congenital hydrocephalus associated with atresia of the outlet
foramina of Magendie and Luschka. It is associated with agenesis of the cerebellar vermis and
agenesis of the splenium of the corpus callosum.

Arnold-Chiari syndrome, a common congenital malformation, is frequently associated with
platybasia and malformation of the occipitovertebral joint; other anomalies frequently seen are
beaking of the tectum, aqueductal stenosis, kinking and herniation of the medulla, and herniation of the cerebellar vermis through the foramen magnum. Meningomyelocele (spina bifida) is
a common component of the syndrome

The posterior neuropore closes during week 4 (day 27). Failure of the posterior neuropore to
close results in lower neural tube defects, such as spina bifida.