6. Limbic lobe
• formed by nested "C-shaped" arches of
tissues surrounding diencephalon, basal
ganglia
7. Outer arch
• Largest of the three arches
• Extends from temporal to frontal lobes, comprised of
- Uncus (anterior end of parahippocampal gyrus)
- Parahippocampal gyrus (swings medially at posterior
temporal lobe, becomes isthmus of cingulate gyrus)
- Cingulate gyrus (anterosuperior continuation of
parahippocampal gyrus)
- Subcallosal (paraolfactory area) is anteroinferior
continuation of cingulate gyrus
• Curves above callosal sulcus (continuous with
hippocampal sulcus of temporal lobe)
8. Middle arch
• Extends from temporal to frontal lobes,
comprised of
- Hippocampus proper (Ammon horn)
- Dentate gyrus
- Supracallosal gyrus (indusium griseum, a thin
strip of gray matter that extends from
dentate/hippocampus all the way around corpus
callosum to paraterminal gyrus)
- Paraterminal gyrus (below corpus callosum
rostrum)
• Curves over corpus callosum, below callosal
sulcus
9. Inner arch
• Smallest arch
• Extends from temporal lobe to mamillary
bodies
• Comprised of fornix, fimbria
11. Hippocampus
• Curved structure on medial aspect of temporal lobe that
bulges into floor of temporal horn
• Consists of two interlocking "U-shaped" gray matter
structures
- Hippocampus proper (Ammon horn) forms more
superolateral, upside-down U
- Dentate gyrus forms inferomedial U
• Has three anatomic subdivisions
- Head (pes hippocampus): Most anterior part, oriented
transversely; has 3-4 digitations on superior surface
- Body: Cylindrical, oriented parasagittally
- Tail: Most posterior portion; narrows then curves
around splenium to form indusium griseum above corpus
callosum (CC)
12. Ammon horn (hippocampus
proper)
• Subdivided into four zones (based on histology of main cell
layers)
- CA1 (Sommer sector): Small pyramidal cells (most
vulnerable; commonly affected by anoxia, mesial temporal
sclerosis)
- CA2: Narrow, dense band of large pyramidal cells ("resistant
sector")
- CA3: Wide loose band of large pyramidal cells
- CA4 (end-folium): Loosely structured inner zone,enveloped
by dentate gyrus
• Blends laterally into subiculum
- Subiculum forms transition to neocortex of parahippocampal
gyrus (entorhinal cortex)
• Covered by layer of efferent fibers, the alveus
- Alveus borders temporal horn of lateral ventricle ventricle
- Forms fimbria → crus of fornix
13. Fornix
• Primary efferent system from hippocampus
• Four parts
- Crura (arch under CC splenium, form part of
medial wall of lateral ventricles)
- Commissure (connects crura)
- Body (formed by convergence of crura,
attached to inferior surface of septum
pellucidum)
- Columns (curve inferiorly to mammillary
bodies,anterior thalamus, mamillary bodies,
septal nuclei)
14. Amygdala
• Large complex of gray nuclei medial to
uncus, just in front of temporal horn of
lateral ventricle
• Tail of caudate nucleus ends in amygdala
• Major efferent is stria terminalis
- Stria terminalis arches in sulcus between
caudate nucleus, thalamus
- Forms one margin of choroid fissure
(other is fornix)
15. Imaging Pitfalls
• Normal variant is incomplete fusion of
hippocampal sulcus → CSF-containing
"cysts" along medial hippocampus
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41. Reference
• Diagnostic and surgical imaging anatomy. Brain, head &
neck, spine /H. Ric Harnsbcrger... [et al.] ; managing
editor, Andre Macdonald. - - 1st ed. p.76-85 ; I cm.
