A macroscopical study of the trapezius muscle of sharks, with reference to the topographically related nerves and vein.

The truncus intestino-accessorius of the vagus nerve, spino-occipital, circumbranchial and, in part, the pectoral spinal nerves of sharks Mustelus manazo were macroscopically studied. The morphological features of these nerves along their courses in the epibranchial region were virtually entirely elucidated. The trapezius muscle of Mustelus sharks, in contrast with that of human beings, was found to be supplied solely by rami accessorii--subbranches of the truncus intestino-accessorius of the vagus nerve; no evidence indicating the direct contribution of the spinal nerves to the innervation of the trapezius were obtained. It was also found that the cutaneous branches of the spino-occipital, circumbranchial and pectoral spinal nerves were distributed in the skin overlying the trapezius and the lateral wall of the branchial basket. Topographical relation of the rami accessorii and the branchial branches of the vagus nerve of sharks to the vena capitis lateralis revealed a striking similarity to the relation of the accessory nerve and the nervus laryngeus superior to the vena jugularis interna of human beings. The morphological concept of 'accessory fork' (Accessorius-Gabel) proposed by Haller seems to be important in considering the hypoglosso-cervical ansa complex, superficial branches of the cervical plexus and the vago-accessorius complex, which reminds us more clearly of the embryological trace of its branchial origin of the human trapezius.