Functional Aspects of the Jaw-Articulation in the North American Badger, with Comments on Adaptiveness of Tooth-Wear

Abstract

While studying skulls of the North American badger, Taxidea taxus, I observed that many old adults possessed mandibles locked in articulation with the glenoid fossae of the squamosals so firmly that each mandible was movable only up or down and that the mandible could be disarticulated from the squamosal only by breaking squamosal bone. Each glenoid fossa (Fig. 1, A-D) was deeply concave in lateral view, fitted for receiving the articular process (or condyloid process) of the ramus of the mandible. This process (Fig. 1, C, E) is developed medially and laterally and is a slender transverse structure smoothly rounded dorsally, posteriorly, and somewhat rounded ventrally. It has the appearance of a cylinder in dorsal view, but in caudal view the medial development is much thicker than the lateral one (Fig. 1, C). The process in caudal view resembles a cone, apex laterad. The long axis (transverse) of the structure is more than four times the width of the posterior part of the ramus. The glenoid fossa, then, is a deep trough-like depression narrowing and extending onto the ventral surface of the squamosal arm of the zygoma (Fig. 1, B). The articular process is free to rotate in this trough only about its long axis. Sideway or lateral movement of the mandible is prevented largely by the inability of either articular process to pivot forward or back, even slightly. The processes are held firmly in place by the lateral narrowing of the walls of the fossae. The dentary-squamosal articulation of the badger is thus a quite idealized pin hinge, identical in function to a door hinge. Grinding accomplished by the molar teeth is restricted in the badger and differs greatly from the grinding function usually observed in mammals (Young, 1963:200-201). However, the functions of crushing and biting certainly are not impaired by this articulation. As the badger ages the anterior lip of the glenoid fossa projects farther ventrad and laps slightly caudad over the narrow lateral part of the process, locking it in but hardly affecting the closing of the jaws. A locking mechanism has been described as more common in the European badger, Meles, than in Taxidea and has been observed occasion-