In mammals, the zona incerta is thought to be involved in a number of behaviors: visceral activity; arousal; attention; and posture and locomotion. These diverse and complex features suggested that the zona incerta functions as a global or integrative node. Nevertheless, despite multiple investigations into its anatomy, physiology, and behavior in a variety of mammals, no specific character identifies the zona incerta besides its appearance in fiber-stained material and its relationship to surrounding structures. One such structure is the thalamic reticular nucleus whose caudal pole often contains some intermingled cells of the zona incerta. In crocodilians, the entopeduncular nucleus abuts the caudal pole of the thalamic reticular nucleus and displays different immunohistochemical properties and soma size when compared with neurons in the thalamic reticular nucleus itself. To determine if neurons in the entopeduncular nucleus differed from those in the thalamic reticular nucleus in Alligator mississippiensis, the entopeduncular nucleus was investigated using Golgi methodology. The morphology and soma size of neurons in the entopeduncular nucleus differed from those in the thalamic reticular nucleus and indicated that these two areas are indeed separate neuronal aggregates. Based on these data and the known relationships of the zona incerta to surrounding structures in mammals, the entopeduncular nucleus of crocodilians is suggested to be the counterpart of the zona incerta of mammals.

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