Page "Temporomandibular joint" Paragraph 40

When the mandible is moved into a lateral excursion, the working side condyle ( the condyle on the side of the mandible that moves outwards ) only performs rotation ( in the horizontal plane ), while the balancing side condyle performs translation.

During actual functional chewing, when the teeth are not only moved side to side, but also up and down when biting of the teeth is incorporated as well, rotation ( in a vertical plane ) also plays a part in both condyles.