Talk:Paper - The Development of the Cranial and Spinal Nerves in the Occipital Region of the Human Embryo

98 Development of Occipital Nerves in Human Embryos

region, as though fragments of this ganglion. The close relation between the first cervical ganglion and this nerve serves to explain the conditions found in the adult. Along the more cranial portion of the nerve there is a row of ganglia, the accessory root ganglia, which become successively larger as we go forward, and which form a series with the ganglion jugulare of the vagus. The number of these accessory ganglia is usually three or four principal masses, and in addition there are several smaller clumps scattered among the rootlets. In a series of pig dissections at the corresponding age it was not possible to determine a true segmental order in their formation, and there was no correspondence between these ganglia,and the number of the hypoglossal roots, and they show no connection with them. Thus they are not to be confused with the occipital ganglia of Froriep. The fibre elements of the accessory nerve fuse with those of the vagus. The occurrence of an actual interchange of fibres between them cannot, however, be determined. Leaving the vagus at the ganglion nodosum the accessory can be traced through the m. sternecleido-mastoideus to the m. trapezius.

The relations of the roots, ganglia, and trunks of the ninth and tenth nerves were seen in the previous stage (Figs. 7, 8, and 9) to have taken on the adult type. In Figs. 11 and 12 the resemblance to the adult conditions is more complete owing to the relative increase of fibre elements. The glosso-pharyngeal nerve arises by several compactly bundled rootlets attached to the neural tube median and caudal to the cartilagenous mass in which the internal ear is embedded. Among these rootlets is the ganglion mass which forms the ganglion of the root or Ehrenritter’s ganglion. Beyond this begins the trunk of the nerve, on which is found a second ganglion, the ganglion of the trunk. It is to be remembered that the ganglion of the root and the ganglion of the trunk have developed separately, and have so far remained discrete structures. From the ganglion petrosum is given off ventrally the tympanic branch, or nerve of Jacobson, and caudally the main trunk of the nerve, which hooks inward and forward toward its terminal distribution. The ninth and tenth nerves lie closely together and there is ample opportunity for anastomosis between them, especially between the ganglia of the trunks. It will be recalled that in a younger embryo (Fig.-4) these ganglia were apparently continuous. .

The vagus presents the same general type as the glosso-pharyngeus; the root and trunk ganglia are larger, and the trunk itself may be traced down into the thorax.

In Fig. 11 the chain of cervical sympathetic ganglia is indicated, and in Fig. 12 is shown their connections with the spinal nerves. The upper