518 PERCIVAL BAILEY 



tutto quello che si e detto per la cavia. Dal velum per diverti- 

 coli lateral! di formano i plessi emisferici inferiori destro e sinistro, 

 dei qiiali uno e disegnato nella fig. 28." 



Finally the author (Bailey, '15) has presented an account of 

 the development of the lateral telencephalic plexus which it 

 is the purpose of the present piper to supplemant. 



Concerning these structures in other groups of vertebrates 

 this discussion is not so much concerned, but a few words at least 

 about the lateral plexus in other vertebrates will not be out 

 of place. This plexus is not present in Teleosts (Burckhardt, '94) 

 nor Anura (Herrick, '10). In Lacertilia its development has 

 been described by Tandler and Kantor ('07) and Warren ('11) 

 and agrees in all essential respects with that hereinafter detailed 

 for Chrj^semys marginata. In examining some young alligators 

 in the collection of Dr. Elizabeth Crosby, the posterior part of 

 the lateral telencephalic plexus was found to be present, but 

 very small and poorly developed. The brain of an adult pigeon 

 was also examined and the lateral telencephalic plexus was 

 seen arising from a plexus formation in the roof of the telen- 

 cephalon, but of the posterior part of the plexus there was no sign 

 except a plexus of blood vessels along a thin but uninvaginated 

 medial hemisphere wall. Dr. C. Judson Herrick suggested that 

 this may represent a stage in the phylogenetic development of 

 the plexus. Mrs. Gage ('95) figures the brain of the embryo 

 of the English sparrow. Both the figures and the context show 

 that the' lateral telencephalic plexuses arise from the median 

 telencephalic plexus and just lateral to the paraphysis, appar- 

 ently not invaginating the medial hemisphere wall. She writes : 

 ''In the young sparrow ( g. 2) the paraphysis occurs in the midst 

 of a mass which gives off the paraplexuses, and it opens directly 

 dorsad of the portas, i.e., into the aula. . . . It is notice- 

 able in the older embryo that 1;he union of the auliplexus with 

 the paraplexuses lies dorsad of the porta (fig. 14)." The works 

 of Neumayer ('99) and Hochstetter ('98) contain nothing of 

 value for the present discussion. The two invaginations which 

 they describe are temporaTy and unimportant. A similar con- 

 dition is shown in my figure 19 (Bailey, '15). D'Erchia ('96) 



