Brain pathways of the brachial nerves of Sepia and Loligo

Abstract

Centripetal cobalt filling of the brachial nerves of Sepia and Loligo gave further information about the afferent and efferent connections of the arms. The supraoesophageal lobes of the brain contain direct motor pathways to the arms. Efferent fibres originate from somata of the inferior frontal ( Loligo ), and ipsilateral and contralateral ( Sepia ), precommissural lobes. In both genera, afferent fibres run to the inferior frontal lobe via ipsilateral and contralateral pathways. Some fibres continue backwards in the interior frontal to palliovisceral tract. In Loligo , further afferent fibres run to the superior buccal, subvertical, precommissural and anterior basal lobes, and in Sepia to the superior frontal lobe. In the suboesophageal lobes, efferent fibres originate in both genera from somata in the anterior and posterior brachial, anterior chromatophore, and anterior pedal lobes. In Sepia , but not in Loligo , efferent fibres pass from the ventral magnocellular lobe direct to the arms. Many afferent fibres run from the arms to end in the brachial lobes, and some ipsilaterally, and a few also contralaterally, to the palliovisceral lobe. The brain pathways of Sepia and Loligo are thus very similar and the few differences are discussed. The magnocellular and palliovisceral lobes contribute less to the innervation of the arms in decapods than in octopods.