Within the wide conformation of skull spectrum, there are generally three recognized broad categories that correspond to the concept of cephalic biotype, determined by the cephalic index. The three cephalic biotypes are: brachiocephalic, mesaticephalic and dolichocephalic, which are based on linear measures. In order to revise this classification based on its geometry, we studied 53 skulls of adult dogs, corresponding to the three craneometric groups previously described: 16 brachycephalic, 20 mesaticephalic and 17 dolichocephalic. Images on ventral plane were obtained and 17 anatomical landmarks were subsequently located and analyzed by means of geometric morphometric techniques. Five of those landmarks corresponded to the neurocraneal area and the rest of the splanchnocranium. The three craneometric groups showed statistically significant differences between them for both size and shape. The variables that contributed to the differentiation between them were located along the edge of the zygomatic arches and on the basis of this arch. Splanchnocranial variables also presented a much more marked allometry than the neurocraneal variables. Since the zygomatic arch should be considered as part of the splanchnocranium, we suggest that the cephalic index (which takes into account the maximum width of the head) is as important as the facial index (which takes into account the maximum width of the face). The neurocraneal index would be much more conservative, and therefore less discriminatory between the groups.
KEY WORDS: Canis familiaris; Cranium; Cranial index; Cephalic index; Mesaticephalic