98 Development of Occipital Nerves in Human Embryos 



region, as thoiigh 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 con- 

 nection 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. sterno- 

 cleido-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 ele- 

 ments. The glosso-pharyngeal nerve arises by several compactly bundled 

 rootlets attached to the neural tube median and caudal to the cartilage- 

 nous 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 wdiich 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 distribiition. 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 3^ounger 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 



