Semicircular Canal Orientation in the Adult Resting Rabbit

Abstract

Photographs of rabbits in the alert resting position were used to record head position. Semicircular canals were surgically exposed and points measured along each canal were used to compute the best-fit plane using a least-squares method. Computations of mean best-fit planes showed that the horizontal canals were not carried horizontally in the rabbit. The anteromedial edges were superior by 16°. The anterior canals were vertically oriented and made an angle of 43° to the sagittal plane. The posterior canal was tipped in the anterior direction slightly and also made an acute angle (26°) with the frontal plane. Rabbit semicircular canals deviated significantly from orthogonality. The range was 86° (anterior canals) to 133° (posterior canals). Thus, there were no co-planar canals. Such semicircular canal geometry has implications for the neural circuitry controlling posture in the rabbit.