The ventral cochlear nucleus was examined in 31 rats' brains prepared according to the protargol method of Bodian. The following regions were delimited on the basis of synaptic, cellular and axonal criteria.
Region II, which occupies the central part of the nucleus, consists principally of cells (type g)which receive modified bulbs of Held from the acoustic nerve and which send large axons to the trapezoid body. The cells were graded in size, the smallest (high frequency) being located dorsally and the larges (low frequency) being located ventrally. Associated with region II are the cells (type b) of the acoustic nerve nucleus. These cells receive boutons from the acoustic nerve and send very large axons to the trapezoid body.
Region IV is located in the posterior part of the ventral cochlear nucleus and is composed of large multipolar cells (type k). The dendrites of these cells are specifically organized with respect to the fibers of the acoustic nerve. Synaptic endings, from the descending branch of the acoustic nerve, consist of boutons on cell body and dendrites. The axons of these cells compose the stria of Held.
Region V is located in the posterior part of the ventral cochlear nucleus and appeared to have only intrinsic connections.
All regions received synaptic endings in addition to those which arose from the acoustic nerve.