648 



terminating in the preoptic recess. Three sulci pass backward from 

 the interventricular foramen (F). The sulcus diencephalicus dorsalis 

 is divided into two parts, the anterior one of which forms the sub- 

 habenular sulcus, while the posterior one bounds an undifferentiated 

 post-habenular region which probably also belongs to the epithalamus. 

 The sulcus diencephalicus ventralis separates the thalamus above from 

 the nucleus preopticus (which is very large in the Amphibia) and the 

 hypothalamus. The preoptic nucleus is bounded in front by a vertical 

 sulcus which closely follows the caudal border of the anterior com- 



/ 



5_accas dorsalis 

 5.shab 



.-.pars dors. thai. 



nc h. 



pars ven.thal. 



'.c~p'ä ' '^" '^' ^- "^'^^ 

 -c.a 



■ n po. pars m . 

 ^— n.po pars ant. 



-■s.ie.ant. 



''•optic chiasma 



Fig. 3. Graphic reconstruction of the median view of the left half of the brain 

 of adult Amblystoma tigrinum after section in the sagittal plane. The line A — B marks 

 the plane of section in Fig. 2. 



c.a. eommissura anterior, com.post. commissura posterior, com.sup. comraissura 

 superior, c.p.a. commissura pallii anterior. F. foramen interventriculare. n.c.h. nucleus 

 of commissura hippocampi (this is Gaupp's nucleus supracommissuralis of the frog). 

 n.po.pars ant. nucleus preopticus, pars anterior, n.poqiars m. nucleus preopticus, pars 

 magnocellulaiis. P. paraphysis. pars dors. thai, pars dorsalis thalami. ^^ars t^e?;. <Äa?. 

 pars ventralis thalami. s.ie.ant. sulcus interencephalicus anterior of Kupffek. s.shah. 

 sulcus subhabenularis (anterior part of sulcus diencephalicus dorsalis). z.lim.mecl . zona 

 limitans medialis, or ventral boundary of primordium hippocampi. 



missure ridge. This is the ventral end of Kupffer's sulcus inter- 

 encephalicus anterior. The preoptic nucleus is divided into anterior 

 and posterior parts by a similar vertical sulcus farther back. The 

 posterior part is homologous with the nucleus magnocellularis strati 

 grisei of fishes and is so designated. 



. The sulcus diencephalicus medius divides the thalamus into dorsal 

 afferent and ventral efferent parts. The former receives the terminals 



