SPINAL ACCESSORY NERVE (part of the sixth pair of the older anatomists ; part of the eighth pair of Willis ; nervus aecessorius ad par vagum ; nervus aecessorius Willisii ; the eleventh pair of Soemmering ; the beinerve of the German anatomists). This nerve is attached to, or, as it is more commonly expressed, arises from, the lateral surface of the cervical portion of the spinal chord close to the posterior roots of the spinal nerves ; and it lies between the pos terior roots of the spinal nerves and the ligamenturii denticulatum. On entering the cranium by the foramen magnum, it continues to receive additional roots or filaments of origin froni the medulla oblongata. It com mences by a very slender filament, most ge nerally opposite the fifth or sixth posterior roots of the spinal nerves, and in its passage upwards to the interior of the cranium, its bulk is gradually increased by additional fila ments of origin from the lateral surface of the spinal chord and from the medulla ob longata. The filaments arising from the spinal chord pass upwards and a little for ward to join the trunk of the nerve, so that it lies a little nearer to the ligamentum den. ticulatum than the attachments of the fila ments forming it. After it enters the cranium by the foramen magnum, it runs forward, outward, and upward, places itself in close apposition to the posterior surface of the par vagum, and escapes from the interior of the cranium, through the foramen lacerum posterius, along with the vagus and glosso pharyngeal nerves. The roots of the acces sory that arise from the medulla oblongata are placed in the same line with the lower roots or filaments of origin of the par vagum; and the upper roots of the former approach so closely to the lower roots of the latter, that it is frequently difficult to say with con fidence where the roots of the one nerve end and those of the other begin. (Fig. 521, 3, 5.) Previous to the time of Willis, anatomists considered this nerve as constituting a part of the vagus, and to him is due the credit of first pointing out clearly the grounds on which its separation from the vagus rests. Very great discrepancy exists in the descrip tion of the origin of this nerve given by the best anatomists. This is explained, not only by the fact first pointed out particularly by Scarpa*, that its filaments of origin are at tached over different extents of the spinal chord in different individuals, and sometimes to a greater extent on one side than on the other in the same individual, but also by its lower roots or filaments of origin being so slender that they sometimes cannot be ac curately traced by the naked eye. Willis himself describes it as commencing by a very slender beginning near the sixth or seventh cervical nerve.f Scarpa ascertained that its lowest root may be attached to the spinal chord opposite the fourth, fifth, sixth, or seventh cervical nerve, but more frequently between the fifth and sixth ; and that when its roots are extended over a more limited por tion of the spinal chord, this is compensated for by their being proportionally stronger.* Anatomists have differed as widely in their account of the particular column or tract of the spinal chord to which the roots of the spinal accessory are attached, as they have done regarding the extent of the spinal chord over which these roots stretch. This is a
point in the anatomy of the nerve which has assumed greater importance since the dis covery by Sir Charles Bell, of the separate functions of the anterior and posterior roots of the spinal nerves, and is of much more interest to the modern, than it was to the older anatomists. The filaments of origin or roots of this nerve that come from the spinal chord are attached to the chord near the posterior lateral groove separating its posterior and middle columns, and close upon the pos terior roots of the spinal nerves, so that we can readily understand how some anatomists should describe these roots as arising from the middle column, and others describe them as springing from the posterior column.± Among the modern anatomists we find Bel lingeri, who has attended particularly' to the anatomy of this nerve, describing it as arising from the middle or lateral column of the spinal chord*, while Bischofft and Bernardt, trace its origin to the posterior column ; and Bendz§ states that while nearly the whole of its roots come from the middle column, a few arise between the posterior roots of the spinal nerves and front the posterior column.II From my own examinations of the attach ments of this nerve, I had arrived at the con clusion that it arises from the posterior part of the middle column, and that its middle and inferior roots are attached along the course of the decussating fibres of the pyramidal column, which form the posterior part of the middle column of the chord.'ll Stilling says** that the lower and middle roots of this nerve can be traced to the anterior grey substances in the chord, from which the anterior roots of the spinal nerves arise, and that, in an anatomical point of view, they must be re garded as performin,Y the same functions as the anterior roots of the spinal nerves ; while the upper roots, or those which are attached to the medulla oblongata, differ in a marked manner, in regard to their origin, from the lower and middle roots. He states that these upper roots above the first cervical nerve arise from a grey mass in the medulla ob longata, which he styles the accessory.hernel (accessorius-kerntt), and that they resemble closely the lower filaments of origin of the par vagum. These upper roots of the acces sory do not arise from the gelatinous sub stance from which, according to Stilling, the posterior roots of the spinal nerves spring, yet they come into closer relation with it the nearer they approach to the commencement of the roots of the vagus. The upper fi bres of the accessory, though not continuous with the posterior roots of the spinal nerves, are yet, he believes, analogous to thesd; and this view is strengthened by their presenting the same connection with the roots of the hypoglossal as is found between the roots of the posterior and anterior spinal nerves at their origin.