The hypothalamus (plural: hypothalami) is located, as the name would suggest, below the thalamus, and is intimately associated with both the limbic system and the pituitary gland.

Gross anatomy

Boundaries

Its boundaries are in some places poorly defined (outlined in blue in Figure 2):

anterior: lamina terminalis, with optic chiasm at its lower border and anterior commissure above
superior: an imaginary line drawn between the anterior and posterior commissures (AC-PC line)
posterior: an imaginary line sloping antero-inferiorly from the posterior commissure to the mammillary bodies
inferior (floor): infundibular stalk, tuber cinereum and mammillary bodies (from front to back)

Fiber tracts

postcommissural fornix: running posterior to the anterior commissure vertically down to end in the mamillary bodies
principal mammillary bundle: originates in the mamillary body and runs superiorly a short distance before dividing into
- mammillothalamic tract (a.k.a. Vicq d'Azyr bundle): terminates in the anterior thalamic nucleus
- mammillotegmental tract (smaller)

Nuclei

The hypothalamus is really a collection of nuclei arranged symmetrically around its floor and lateral walls and can be divided into medial and lateral areas.

Medial area

supraoptic (anterior)
- supraoptic nucleus (medial part)
- suprachiasmatic nucleus
- medial preoptic nucleus
- paraventricular nucleus
- anterior nucleus
tuberal
- dorsomedial nucleus
- ventromedial nucleus
mammillary (posterior)
- mammillary nuclei
- posterior nucleus

Lateral area

supraoptic (anterior)
- lateral preoptic nucleus
- supraoptic nucleus (lateral part)
- lateral nucleus (anterior part)
tuberal
- lateral nucleus (tuberal part)
- lateral tuberal nuclei
mammillary (posterior)
- lateral nucleus (posterior part)

Blood Supply

Anterior: branches of ACA and ACOM
Tuberal: branches of PCOM and superior hypophyseal artery
Posterior: branches of PCA
Infundibulum: superior hypophyseal arteries from the ophthalmic branch of ICA (C6)