Studies in functional and analytical craniology. 9. The comparative and evolutional outlook.

Abstract

In this paper an attempt is made to reach some general conclusions based on the descriptive, analytical, and comparative material gathered in Parts I-VIII of this series (Tucker 1954a-f, 1955a, b). The type of mastication is an important morphogenetical factor for all skulls with fixed (circumscribed) stresses. In the skull with dispersed stresses the morphogenetic influence of the splanchnocranium on the neurocranium is much smaller than in the skulls with fixed stresses. Consequently, the skulls with fixed stresses demonstrate typological, structural, and functional uniformity, while the development of neuro- and splanchnocrania in the skulls with dispersed stresses may follow various morphoevolutional directions. The importance of this fact in the evolution of man is briefly discussed. The development of the human neurocranium is made possible by the technique of mastication, among other factors. The type of mastication practised is much less varied than the diet. Accordingly, it has much greater morphogenetical consequence. It is suggested that the relations between environment and structure may occur only by means of function. Function influences the internal structure as well as affecting the environment. The morphofunctional influences of the type of mastication are discussed, using as an example the skulls of Lemuroidea. The functional analysis of the masticatory movements in Smilodon was used as an illustration of the transformative possibilities and their limitations connected with steno- and euryfunction. The stenofunctional animal can achieve morphological metamorphoses only through primary intraorganismic changes. The formation and evolution of nodes from the primitive planoarcuate skull to the morphology of the breviarcuate, longoarcuate, and planoarcuate skulls are also demonstrated (cf. Table 1). The comparative morphology and topography of the supraorbital node, the fronto-premaxillary connections, the maxillary, and squamosal nodes as well as the interparieto-occipital node are given. Relations to the craniological investigations of other workers are discussed.