On the nerve plexus of the chicken gizzard.

The Auerbach's plexus of the gizzard was stained in toto in adult chicken and in young and newly-hatched chicks. The plexus lies immediately beneath the serosa and extends over 55% of the surface of the organ, covering its cranial and caudal poles and the two curvatures. The areas into which the plexus does not extend (i.e., most of the ventral and the dorsal surface) are those where the muscle is covered by the laminar tendon of the gizzard. The ganglia are large, often with hundred of neurons, and have short and broad connecting strands. They are surrounded by a capsule of connective tissue. The ganglion neurons are discoidal and in the adult they measure up to 50 microns in diameter, each being surrounded by a set of glial cells. A few small neurons persist in the adult; in the newly-hatched chick these are predominant, but some large neurons up to 25 microns in diameter are already present. The ultra-structural features of the ganglia of the Auerbach's plexus include the abundance of axo-somatic synapses, as well as numerous axo-dendritic synapses, the presence of intra-ganglionic bundles of collagen fibrils and blood vessels, the abundance of glial cells. In addition to the plexus beneath the serosa, the gizzard has many small intramuscular ganglia located throughout the musculature (which is exclusively circular). These ganglia do not have a connective tissue capsule and are made of small and tightly packed neurons.