Movements of the forelimbs of the cat during stepping on a treadmill.

In normal cats stepping on a treadmill an analysis has been made of movements of the scapula, shoulder, elbow, wrist and digits. The scapula is capable of making large and complicated movements over the rib cage. In locomotion they may be resolved into a cyclical, similunar movement of the glenoid cavity in the parasagittal plane of the cat's body. The movements of the scapula are rather constant over a wide range of velocities. They most resemble those of the hip which also shows a delay in the onset of extension and no yield phase. It is suggested that movements of the scapula have a high priority in the execution of locomotion in the forelimbs. The movements at the shoulder tend to parallel those of the elbow. The terms of palmar flexion and dorsiflexion are retained for the movements at the wrist and digits. The rapid phase of palmar flexion corresponds with the flexion phase at the elbow, and the phase of dorsiflexion with the first extension phase at the elbow. Palmar flexion during the second and third extension phases of the more proximal joints would appear to be initiated by contact of the foot with the ground. The sequences of movement at the wrist and digits allow a comparison of the roles of flexor and extensor muscles of the forearm during locomotion and the flexion reflex, which is compatible with the functional and anatomical organization of cervicothoracic segments. With exception of extension at the scapula the movements of the elbow provide an index of the onsets of flexion and extension at the other joints of the forelimb. Modifications are suggested for the Phillippson step cycle of both forelimbs and hindlimbs to include the delayed onset of extension at the scapula and hip and the particular movements of the wrist, digits and toes.