Figure 4. Frontal views of an ontogenetic series of horn core growth within Ovis. A, Ovis canadensis, 2-3 months old (PLWZM UM 7927); arrows locate the incipient horn core developments on the frontals. B, Ovis dalli, female, 11.5 months old (PLWZM UM 11688); horn cores are wider than long and are posteriorly directed (arrow). C, Ovis canadensis, male, 5 months old (PLWZM UM 6307); horn cores are better developed than on the female in B; horn cores (arrow) are still wide for their length, and show incipient torsion (outward turning). D, Ovis dalli, female, adult (NAUQSP 2780); horn cores are fully developed and directed posteriorly without torsion. E, Ovis canadensis, male, adult (NAU QSP 7325); note the torsion of the horn cores. Scale bars equal 10 mm.