Logarithmic growth of the hominoid mandible

Abstract

The growth of the basal unit of the mandible was studied by plotting the position, relative to the median plane, of the oval, mandibular and mental foramina in immature and adult skulls of Man, chimpanzee and gorilla. In Man, the basal unit was found to grow out along a constant logarithmic spiral. In the apes, the basal unit grew along a constant logarithmic spiral, the amount of unfolding being greater in the gorilla than in the chimpanzee. It is argued that the mode of growth seen in the apes evolved, as these forms became more prognathous, because it requires less compensatory rotation of the mandible, while the mode seen in Man is probably closer to that which occurred in common ancestral form.

Developmental changes in the shape of the supralaryngeal vocal tract in chimpanzees

“…However, plexiform bones, which indicate rapid growth in a given site, are present in the posterior border of the ramus in chimpanzees (Johnson et al, 1976) but not in humans (Atkinson and Woodhead, 1968). Comparisons using dental stage showed that the acceleration of the superior-inferior growth of the mandible is as great in chimpanzees as in humans in the infant stage, but is less in chimpanzees in the elder stage (Hildyard et al, 1976). These facts indicate that the mandible grows more rapidly but is shorter in the superior-inferior dimension in chimpanzees than in humans.…”

Investigation of Mandibular and Neurocranial Form

“…As other skeletal units, the mandible is markedly var iable [Purzansky, 1969;Colien, 1981] being affected by an array of factors including genetic [Festing, 1974;Goto et al, 1979], tooth size [Lucas, 1982], body size [Turner, 1978], growth [Hildyard et al, 1976], masticat ory muscle function [Kantomaa and Ronning, 1982], lip pressure [Baradch et al, 1984], head posture [.S'o/rnv and Tallgren, 1976] and evolutionary change [Wolpoff, 1977]. Until the relative effects of these and other fac tors on mandibular form have been partitioned [Festing, 1976;Steinberg, 1981;Hendricksen et al, 1982], how ever, accurate prediction of growth or the effects of orthognathic surgery will remain elusive [Bell and Scheideman, 1981;Oxnard, 1978;Dormer, 1980].…”