Objectives: Porotic hyperostosis, characterized by porotic lesions on the cranial vault, and $cribra\; orbitalia$, a localized appearance of porotic lesions on the roof of the orbits, are relatively common osteological conditions. Their etiology has been the focus of several studies, and an association with anemia has long been suggested. Anemia often causes bone marrow hypertrophy or hyperplasia, leading to the expansion in trabecular or cranial diploic bone as a result of increased hematopoiesis. Hypertrophy and/or hyperplasia is often coupled with a disruption of the remodeling process of outer cortical bone, cranially and/or post-cranially, leading to the externally visible porotic lesions reported in osteological remains. In this paper, we investigate whether individuals with cribra orbitalia have increased thickness of the diploë, the common morphological direct effect of increased hematopoiesis, and thus test the relationship between the two conditions, as well as explore the type of anemia that underlie it. Methods: An analysis of medical CT scans of a worldwide sample of 98 complete, young to middle-aged adult dry skulls from the Duckworth Collection was conducted on male and female cribrotic individuals (n= 23) and non-cribrotic individuals (n= 75), all of whom lacked any evidence of porotic lesions on the vault. Measurements of total and partial cranial thickness were obtained by virtual landmark placement, using the Amira 5.4 software; all analyses were conducted in IBM SPSS 21. Results: Cribriotic individuals have significantly thinner diploic bone and thicker outer and inner tables than non-cribriotic individuals, contrary to the expected diploic expansion that would result from anemic conditions associated to bone marrow hypertrophy or hyperplasia. Additionally, individuals without cribra orbitalia and those with the condition have distinctive cranial thickness at particular locations across the skull and the severity to which cribra orbitalia is expressed also differentiates between those with mild and those with a moderate to severe form of the condition. Conclusions: Our results suggest a complex pattern of causality in relation to the pathologies that may lead to the formation of porotic lesions on the vault and the roof of the orbits. A form of anemia may be behind the osteological changes observed in porotic hyperostosis and cribra orbitalia, but it is unlikely to be the same type of anemic condition that underlies both types of osteological lesions. We suggest that cribra orbitalia may be associated to anemias that lead to diploic bone hypocellularity and hypoplasia, such as those caused by anemia of chronic disease and, to a lesser extent, of renal failure, aplastic anemia, protein deficiency and anemia of endocrine disorders, and not those that lead to bone marrow hypercellularity and hyperplasia and potential porotic hyperostosis. This leads us to the conclusion that the terms porotic hyperostosis and cribra orbitalia should be used to reflect different underlying conditions.