276 C. W. PRENTISS 



hypoglossal. Anterior to these three ganglionic masses is a large 

 ganglion elongate in the line of the ganglionic crest. Five groups 

 of proximal roots arise from the myelencephalon and distal roots 

 join the spinal accessory. The anterior of these is the largest. Soon 

 after it unites with the spinal accessory a short very slender cord 

 of cells and fibers passes over to the jugular ganglion (fig. 7, x). 

 This is the only connection between the hypoglossal ganglia and 

 the jugular ganglion of the vagus. 



The hypoglossal ganglia are best developed in the 17 mm. em- 

 bryo shown in fig. 6. In this case three distal roots join the hypo- 

 glossal from as many ganglia, and a fourth distal spur is present. 

 The first cervical ganglion is only partially divided. Comparing 

 the hypoglossal ganglia with one division of the first cervical gang- 

 lion as seen in fig. 4, the resemblance is plain. 



From ten dissections at this stage we would note the following- 

 points: (1) The hypoglossal ganglia here reach their highest 

 differentiation; (2) in every case Froriep's ganglion was present 

 with a well developed hypoglossal root, — in three cases two such 

 hypoglossal roots were present, in one case the ganglion was forked 

 and in one case (fig. 6) there was evidence of four hypoglossal 

 ganglia with distal roots ; (3) this stage proves that the connec- 

 tion between the jugular ganglion and the hypoglossal ganglion 

 is of little importance other than showing that both are derived 

 from a common neural crest ; (4) as observed in preceding stages, 

 there is great variation in the hypoglossal ganglia of different 

 individuals, and on the two sides of the same embryo; no two 

 were exactly alike; (5) the root of the spinal accessory could be 

 traced back to the eighth cervical ganglion. 



Stage 5. 28-30 mm. In succeeding stages the hypoglossal 

 ganglia show retrogressive changes as to structure and relative 

 size. Fig. 8 shows the persistence of a single hypoglossal gang- 

 lion (Froriep's) posteriorly. Anteriorly three closely connected 

 ganglia are seen, the more posterior sending a spur backward, 

 which ends abruptly. This condition was found in two cases. 

 In one case a double hypoglossal ganglion was present, and in 

 one case a small spurred fragment occupied a position near the 



