103 Developnieiit of Occipital Nerves in Human Embryos 



ration that would be artificial; they will therefore be described together. 

 The hypoglossus and the cervical nerves, where a close relation also exists, 

 will be likewise treated. 



The Glosso-Pharyngeal Nerve from the beginning possesses the char- 

 acteristics of a mixed nerve. In embryos 4.0 mm. long (Fig. 1) it 

 consists of a small clump of ganglionic cells, which can be distinguished 

 in the mesenchyma attached to the neural tube just caudal to the otic 

 vesicle and extending toward the third branchial arch. This group of 

 cells represents the anlage of the ganglion of the root, or Ehrenritter's 

 ganglion. Among these cells are a few fibroblastic processes, which do 

 not belong to them, but arise from cells of the neural tube in the dorsal 

 part of the ventral zone of His, and form the motor elements of the root. 

 The character of this anlage resembles that of the vagus; and may be 

 regarded as a part of the ganglion crest of the after-brain, though it is 

 not continuous with the vagal portion of it. It is evident that this 

 ganglion is not a part which has become separated off from the ganglion 

 petrosum as described by Henle, and others (see Thane, 95), but is an 

 independent structure. Its inconstancy is to be explained by its further 

 development. It reaches a size early in the embryo at which it ceases to 

 further develop, in some embryos earlier than others. The fibre elements, 

 however, continue to grow, and finally overgrow the ganglion and thus 

 cause it to be apparently absent. A similar occurrence will be seen in 

 case of the root ganglia of the accessory nerve. 



Ventral to this group of cells is a somewhat larger clump of cells, the 

 primitive ganglion petrosum, which is situated directly beneath the epi- 

 dermis at the caudal and dorsal margin of the second gill cleft (see Figs. 

 1, 2, and 3). At this time it is separated from the rest of the anlage 

 of the ninth by a looser zone of cells, and this gives it the appearance of 

 having developed in situ, rather than of being a subdivision or bud from 

 the rest of the anlage. It is true that the same appearance might arise 

 from a migration of cells from the latter followed by a proliferation of 

 them at this point. The position of the ganglion petrosum here and in 

 older embryos (Figs. 4, 5, and 6) indicates a close relationship between 

 it and the branchial arches, and the same is likewise true of the ganglion 

 nodosum. In this respect the anlages of the ganglia of the trunks differ 

 from the ganglionic crest proper, or anlage of the root ganglia, which 

 is well removed from the branchial arches and does not show any trace of 

 branchio-meric arrangement. This suggests a difference in origin to exist 

 for the two kinds of ganglia. Another point of difference between the 

 ganglia of the roots and the ganglia of the trunks of these nerves is the 



