Question: There is a loss of motor function of the short abductor and opponens pollicis, combined with wasting at the site of these two muscles in the lateral part of the ball of the right thumb.

Why may exclude a lesion of the spinal nerve proximal to its division into the ventral and dorsal primary rami?

Why may we rule out a central lesion? Approach this response by considering what roots or trunks of the brachial plexus would have to be involved?