458 C. JUDSON HERRICK 



lateralward along those fibers of the fimbria which enter the com- 

 missura pallii posterior (figs. 56 and 57). This nucleus I term 

 the nucleus of the commissura pallii posterior. It clearly is a 

 part of the precommissural body. Thus the commissura pallii 

 posterior, like all of the commissures in the lamina terminalis, 

 is embedded in a matrix of cells belonging to the precommis- 

 sural body, though in this case these cells lie far laterally and not 

 in the velum trans versum itself. 



The relations of the commissura pallii posterior to the precom- 

 missural body were first described by Elliot Smith ('03) in Spheno- 

 don and lizards. Two embryos of Sphenodon in the Harvard 

 Collection permit a re-examination and full confirmation of his 

 description. Figs. 58 and 59 pass horizontally through the cross- 

 ing of the commissura pallii posterior in the velum transversum 

 in an embryo of 25.2 mm. Fig. 58 shows the nucleus of the com- 

 missure at its greatest extent and lying much nearer the mid- 

 line than in Lacerta. Fig. 59 is 70 micra farther dorsal nnd illus- 

 trates its farthest extension into the fimbria. The relation of 

 the nucleus to the precommissural body is broader and more 

 evident than in Lacerta and similar in plan. 



Kupffer ('06) has described the brains of advanced embryos of 

 Anguis fragilis in which the structure of the septum is clearly 

 brought out. In fig. 60 I present a copy of his drawing of a sec- 

 tion through the lamina terminalis. The precommissural body 

 is very large and is termed eminentia medialis. At the level fig- 

 ured it is divided into a ventral part forming the commissure bed 

 (tr.), a lateral part (em.), the nucleus lateralis septi, and a dorsal 

 mass (m'). These relations conform very closely to those of the 

 lizard embryo (fig. 54). Kupffer's nucleus, m, which he re- 

 gards as part of the septum and identifies with Gaupp's gan- 

 glion septi of the frog, is the primordium hippocampi and his 

 fissure (J.c.h.), is the fissura limitans hippocampi of my description. 

 A section taken through the commissura pallii posterior shows 

 an "unbekannter Kern" (Kupffer's fig. 259, k) which is clearly 

 the nucleus of this commissure, as described above for Lacerta. 



Figs. 61 and 62 illustrate transverse sections through the brain 

 of an adult lizard, Plnynosoma, the so-called horned toad of the 



