Pourfour du Petit's experiments on the origin of the sympathetic nerve.

POURFOUR DU PETIT iS of interest in the history of neuroanatomy for his observations and controlled experiments which led to the correction of the earlier view that the 'intercostal nerve' is of cranial origin. The so-called intercostal nerve was the name which had been given by Thomas Willis to the sympathetic chain. This, of course, is one of the two divisions of the autonomic system which innervates smooth muscle and glandular tissue. It has now been known for many years that the preganglionic fibres of the sympathetic chain have their superficial origin in thoracic and lumbar segments of the spinal cord, and that it is only as an extension from the thoracic chain that sympathetic branches find their way into the neck and structures of the head. Stretching downwards from its uppermost ganglion in the neck the sympathetic trunk, when open to view, resembles a skein of loose crochet-work. On entering the thorax it veers backwards to follow the spinal curve, but as it descends behind the pleura, it generally inclines forwards from the heads of the ribs on the sides of the vertebrae, ganglia being studded at intervals along its length. Morgagni's early eighteenthcentury engravings which depict the draping of the sympathetic nerve down the back of the empty thorax conform well to this description.' In relation to the ribs, Willis's name 'intercostal' was not appropriate; it was a transcostal nerve. His mistaken notion, however, about the cranial origin of this nerve, was, as we shall presently see, pardonable enough. As we are informed in any modem textbook on anatomy, all the cranial nerves except the first, second and eighth receive postganglionic fibres, either directly or indirectly, from the sympathetic trunk. Fibres from the side of the superior cervical ganglion of the sympathetic trunk extend directly to the hypoglossal nerve and to the inferior ganglion of the vagus nerve. Also a short ascending jugular nerve divides into twigs which reach the superior ganglion of the vagus and the inferior ganglion of the glossopharyngeal nerve. Other cranial nerves-the oculomotor, the trochlear, the abducent, and the ophthalmic division of the trigeminal-receive sympathetic twigs indirectly in the cavernous sinus from the internal carotid plexus, the net-like ramification round the internal carotid artery which is formed from the postganglionic branch of the upper pole of the superior cervical ganglion. The fundamental error of such earlier anatomists as Willis and Vieussens was in describing these fibres between the carotid plexus and certain cranial nerves as emerging from them, rather than as verging into their branches and sharing common sheaths. In its grosser form, this misunderstanding was corrected by Pourfour du Petit. Fran9ois Pourfour du Petit-to be carefully distinguished from his contemporary