HYPOGLOSSAL GANGLIA OF PIG EMBRYOS 281 



3. According to their development, the hypoglossal ganglia 

 can be divided only artificially into a cephalic cerebral group and 

 a caudal pre-cervical group. 



4. The first cervical and other spinal ganglia are often of 

 double origin, composed of two spindle-shaped masses, and gen- 

 erally possess two distal roots. 



5. The spindle-shaped ganglion of Froriep with its single 

 distal root would therefore represent but one half of a spinal gang- 

 lion. 



6. The degree of development of the hypoglossal ganglia 

 varies in different embryos ; in the same embryo the right side may 

 be better developed than the left, and vice versa. This is good evi- 

 dence of their rudimentary or vestigial character. 



7. One, frequently two or three, and in one case four hypo- 

 glossal ganglia possessed single distal roots and the fibers of three 

 of these joined the hypoglossal nerve. 



8. The connection of the hypoglossal ganglia with each other 

 and with the jugular ganglion represents a persistence of the neu- 

 ral crest. It is similar to the connections which were found per- 

 sisting between the roots of the spinal ganglia. 



9. If we consider a pair of hypoglossal ganglia as the equiva- 

 lent of a single spinal ganglion, four such ganglia would be repre- 

 sented in pig embryos, between the jugular and the first cervical. 



10. The hypoglossal trunk develops as five or six separate 

 ventral roots, at first parallel and independent, later uniting to 

 form a single nerve. 



11. The hypoglossal ganglia reach their maximum develop- 

 ment in embryos 17-20 mm. long, then retrograde, though gang- 

 lia at both ends of the series may persist in the adult. 



12. The spinal accessory nerve develops very early, being well 

 formed in the youngest embryos examined (5 mm. long). As 

 development proceeds the fibers of the spinal accessory root may 

 be recognized farther and farther caudad. In a pig of 17 mm. a 

 few accessory fibers were traced to a point opposite the eighth 

 cervical ganglion. 



THE JOURNAL OF COMPARATIVE NEUROLOGY AND PSYCHOLOGY, VOL. 20, NO, 4. 



