OBJECTIVE: To define the source and the course of the articular branches to the midthoracic zygapophysial ("z") joints. DESIGN: Cadaveric dissection. SETTING: The Gross Anatomy Laboratory of the Duke University School of Medicine. SUBJECTS: Ten human cadaveric thoraces. METHODS: Gross and stereoscopic dissection of dorsal rami T4-T8 was performed bilaterally on 10 adult embalmed cadavers. The medial and lateral branches were traced to their origins from the dorsal rami, and the course of the articular nerves was documented through digital photography. Radio-opaque wire (20 gauge) was applied to the nerves. Fluoroscopic images were obtained to delineate their radiographic course with respect to osseous landmarks. RESULTS: Forty-eight inferior articular branches were identified. Three (6.3%) originated from the medial branch and 44 (91.7%) from the dorsal ramus. One was indeterminate. Fifty-one superior articular branches were identified. Eight (15.7%) originated from the medial branch and 43 (84.3%) from the dorsal ramus. In 12% of cases (6/50), there was side-to-side asymmetry in the origins of the articular branches. Nerves were commonly suspended in the intertransverse space. The articular branches contacted an osseous structure in only 39% of cases. As previously reported, a "descending branch" was not identified in any specimen. CONCLUSIONS: Articular branches to the T4-T8 z-joints have substantial inter- and intraspecimen variability of origin. They typically arise from the dorsal ramus rather than the medial branch and frequently do not contact any osseous structure to allow percutaneous needle placement.