The brachial plexus of the okapi showed the evolutionarily intermediate status between the underived ruminants and the giraffe with elongated neck. Whereas the C6 was the thinnest among the roots of the brachial plexus, the C7, C8 and T1 were much thicker in the okapi. From the data we concluded that the okapi was equipped with the intermediate characteristics of the disappearing C6. Although the nerve of the C6 should be elongated in accordance with the long neck in the Giraffidae, the extraordinary elongation of the C6 may have no advantages in the function of the innervations. In the okapi, therefore, we suggest that the function of the C6 has been mainly replaced with that of C7.