A young woman is evaluated by a neurosurgeon because of injuries she received in an explosion. She has numerous lacerations of the front and back torso and bruising of the craniofacial region. Neurological examination shows lack of movement in her right lower extremity with hyperreflexia, and loss of proprioception and fine touch in this extremity, but pain and temperature sensation are intact. Pain and temperature sensation are absent in the left lower limb. Movement and reflexes are normal in the left lower extremity and upper extremities. A lesion in which of the following locations can explain her neurological examination?