HYPOGLOSSAL GANGLIA OF PIG EMBEYOS 269 



neural crest (crist. new.), extending forward to the jugular gang- 

 lion of the vagus (gang, jugul.). Opposite the posterior root of 

 the hypoglossal a marked ventral loop and thickening in the crest 

 (gang. Froriep) shows the position of Froriep's ganglion. An- 

 teriorly the crest of cells is broader and a Tew short proximal 

 rootlets are present. A depression separates it more or less com- 

 pletely from the cells of the jugular ganglion which is flattened 

 and diffuse with 8-10 short proximal roots. The glossopharyn- 

 geal is short and its superior ganglion is joined to the jugular 

 ganglion by a small cord of cells. 



The remarkable features at this stage are then: the early 

 development of the spinal roots; the resemblance of the hypo- 

 glossal to a series of ventral spinal roots; the existence of a nearly 

 undifferentiated neural crest between the jugular and the first 

 cervical ganglion. 



Stage 2. 8.5-9 mm. In embryos of this stage (figs. 2 and 3), 

 the roots of the spinal nerves are longer and more fibers are devel- 

 oped. The first cervical ganglion is distinctly double in fig. 2. 

 It is still connected with the second cervical ganglion by a loop 

 of cells. The neural crest between the first cervical and the jug- 

 ular ganglia shows the most marked change. The slight enlarge- 

 ment opposite the posterior root of the hypoglossal which we 

 saw in the first stage has now grown to be a spindle-shaped mass 

 of cells (gang. Froriep) with two proximal roots and a distal 

 bundle of fibers which extends to the root of the hypoglossal. 

 This ganglion (Froriep's) is still connected with cellular loops 

 (nod.) of the neural crest, but in this respect it does not differ from 

 the cervical and sacral ganglia of this stage. It strongly resem- 

 bles one of the two cell masses composing the first cervical gang- 

 lion. Anterior to it is a smaller mass of cells (gang, hypogl.) 

 from which a proximal root is developing. This is the "terminal 

 knob" of the "commissure" figured by Lewis in the 12 mm. pig 

 (1903, pi. I). Anteriorly the crest shows five diffuse irregular 

 cell masses which become gradually larger toward the jugular 

 ganglion with indications of proximal roots. The jugular gang- 

 lion is of more definite form and is pointed ventrally. Dorsal 



