The dorsal retinaculum of the wrist consists of two layers: the supratendinous and the infratendinous. The infratendinous layer is limited to an area deep to the ulnar three compartments. There are six compartments for the tendons dorsal to the wrist separated by six longitudinal vertical septa. Each septum originates from the supratendinous retinaculum and inserts onto the radius. The sixth compartment for the extensor carpi ulnaris is complex. The tendon of the extensor carpi ulnaris is enclosed in an independent fibrous tunnel formed by the supratendinous retinaculum superiorly, the infratendinous retinaculum inferiorly, the sixth septum laterally, and the ulnar insertion of the retinaculum reinforced by longitudinal fibers called the "linea jugata" medially. Our findings support the concept of an adaptable dynamic collateral ligament system rather than the traditional radial and ulnar collateral ligaments.