The dinosaur Diplodocus has a single, relatively large external bony narial orifice that is positioned far back between the orbits. In some mammals, such as elephants and tapirs, the caudal position of the narial opening is associated with a proboscis, so it has been suggested that Diplodocus possibly also had a trunk. In elephants, the facial nerve is large as it emerges from the brain. A branch of this nerve and a branch of the trigeminal nerve unite to form the proboscidial nerve that supplies the muscles of the powerful and complex motor system of the trunk. In contrast to the situation in modern elephants, the absolute as well as the relatively small size of the facial nerve in Diplodocus (deduced from an endocranial cast) indicates that there is no paleoneuroanatomical evidence for the presence of an elephant-like proboscis in this genus.