The median and lateral substantia gelatinosa in the cervical cord of the musk shrew (Suncus murinus) and its synaptic composition.

The extent and laminar arrangement of the substantia gelatinosa (SG) were examined in the cervical spinal cord of the shrew. Between C1 and C6 or C7 the three dorsal layers on either side of the gray matter were confluent at the commissura posterior grisea in shrews of both sexes. Lamina I was thin with no large marginal cells. Lamina II comprised the major part of the SG, consisting of outer cellular and inner neuropil layers. Lamina III was composed of a meshwork of axon terminals, dendritic profiles and myelinated fibers. Unlike the situation in other mammals, in shrew the incidence of axon terminals with round vesicles was similar in the three uppermost layers, but the occurrence of terminal profiles with flat vesicles was significantly greater in deeper laminae. Lamina IV was restricted to the dorsal horn and did not extend through the midline.