Central pathways of the nerves of the arms and mantle of Octopus

Abstract

Centripetal cobalt filling of a brachial nerve of Octopus gave further information about the organization of its tactile learning system. Efferent fibres pass from the posterior buccal and subvertical lobes direct to the arms. Afferent fibres from the arms pass to the lateral and median inferior frontal lobes, others to the lateral and median superior frontal lobes, and a third set to the subvertical lobe. None reach to the vertical or subfrontal lobes. Many somata and afferent fibres were filled in the magnocellular lobes after filling either the brachial or pallial nerves. This is probably a region from which escape reactions are initiated. The lower part of the median basal lobe also receives afferents from both these nerves and a few somata were filled at the lower edge of this lobe. It probably controls the magnocellular lobe, lying below it. After filling of a brachial nerve, or the pallial nerve, somata were filled in both the anterior and posterior chromatophore lobes, but few or no afferent fibres were filled in these lobes. After filling of a brachial nerve many somata and afferent fibres were filled in the prebrachial and brachial lobes and in the anterior pedal lobe, and many fine afferent fibres and a few somata were filled in the superior buccal lobe. After filling of the pallial nerve some filled fibres run forwards to the brachial lobe, but no somata were filled there. No filled fibres from either the brachial or pallial nerves were seen proceeding towards the optic lobes.