Classification of the neurons in fowl hypothalamic nuclei based on their dendritic patterns.

1. Dendroarchitectonic analysis of the hypothalamic nuclei in the fowl was investigated by the Golgi-Cox, Nissl and silver impregnation techniques. 2. All hypothalamic nuclei appeared to consist of leptodendritic neurons constituting a variety within the isodendritic family. They showed triangular, spindle and round shapes and had a few long, relatively straight, fine dendrites bearing very fine dendritic spines. 3. Neurons in the nucleus preopticus medialis et lateralis showed a bipolar spindle-shape and had stout, relatively long primary dendrites. 4. Those in the nucleus hypothalamicus rostralis medialis et lateralis were characterised by bipolar, spindle-shaped and multipolar leptodendritic neurons and by short fine primary dendrites bifurcating to fine longer secondary segments. 5. Neurons in the nucleus hypothalamicus caudalis medialis et lateralis and nucleus hypothalamicus inferior were of the multipolar leptodendritic type and had thick, long, unbranching dendrites emerging directly from the cell body. 6. The fowl hypothalamus is dendroarchitectonically divided into preoptic, rostral and caudal hypothalamic regions; the borderlines separating them are the commissura rostralis and the region between the nucleus hypothalamicus rostralis medialis and nucleus hypothalamicus caudalis medialis, respectively.