Despite the development of innovative approaches and the general success that has been achieved with spinal fusion, the rate of nonunion in some studies has been reported as high as 35%. Decortication has been shown to promote the fusion process and provides not only a rich source of vascular supply from the underlying cancellous bone, but also access to pluripotent stem cells within the marrow. Although the blood supply to the lumbar spine has been described, little attention has been paid to relevant areas of the spine most affected by decortication during the posterolateral fusion process. To assess these areas of the spine and attribute some potential importance to spinal fusion outcome, a perfusion study was designed to delineate the vascular anatomy involved in a decortication procedure. Cadaver spines were perfused with a radiopaque contrast material, fixed, decalcified, and cleared en bloc by the method of Spalteholz. Transverse, sagittal, and coronal slabs were made and the vascular supply was documented. The dominant intraosseous architecture of the vertebra reflected a cancellous bone structure, characterized by marrow and a sinusoidal blood distribution within a trabecular matrix. A contrasting architecture could be differentiated in the pars interarticularis that was more consistent with dense, cortical bone. Matrix from this region typified haversian lamellar bone and exhibited parallel osteons that contained a central vascular component. The relevance of this variance could have multiple implications, given the differences between cortical and cancellous bone in function, formation, healing, and remodeling. In posterolateral intertransverse process arthrodesis, the transverse processes and lateral facets are good areas to be decorticated, whereas the pars interarticularis is less attractive.