224 C. JUDSON HEREICK 



it will be avoided here. The decussations below the fovea will 

 be called the ventral tegmental commissure, and those above 

 the fovea will be called the commissure of the tuberculum pos- 

 terius on account of their proximity to that landmark. This 

 latter commissure is a very complex system and includes, among 

 other elements, postinfundibular hypothalamic fibers of the de- 

 cussatio hypothalamica posterior. The interpeduncular nucleus 

 ventrally of the commissure of the tuberculum posterius is 

 not well developed, but caudad of the fovea isthmi the cor- 

 responding nucleus is very extensive, this region receiving most 

 of the terminals of the tractus habenulo-peduncularis (fascicu- 

 lus retroflexus of Meynert). 



Extending from the tuberculum posterius forward and dorsal- 

 ward on each lateral wall of the brain is a ventricular eminence 

 of considerable extent which extends as far forward as the 

 caudal end of the pars ventralis thalami from which it is sep- 

 arated by a sharp sulcus. This eminence is termed the nucleus 

 of the tuberculum posterius (figs. 7, 8, 9, 23, 24, 29, 30, 47, 59, 

 63, 64, nuc.tuh.p.). The nucleus of the posterior commissure 

 and fasciculus longitudinalis medialis lies partly within the 

 dorsal part of this eminence, but mostly farther dorsally (see 

 p. 271 and figs. 8, 23, 60, nuc.com. post.). 



At the caudal end of the tectum mesencephali there is a 

 broad dorso-lateral eminence formed by the nucleus posterior 

 tecti (figs. 14, 52, 53, nuc.p.t.). In larval urodeles generally 

 there is in this region a lateral dilation of the ventricle, the 

 recessus posterior mesencephali. This is illustrated in a 24 mm. 

 embryo of Necturus by Kupffer ('06, fig. 187; for these rela- 

 tions in larval Amblystoma see my paper, '14 a, p. 353 and figs. 

 1 to 6). In adult Necturus the recess is contracted except 

 under the extreme caudal end of the tectum, where the roof is 

 thin and non-nervous, forming a small velum medullare anterius 

 (fig. 62, v.m.a.). 



As we have already seen, the cerebral peduncle is bounded 

 caudalward by the isthmic fissure externally and the isthmic 

 sulcus internally. Below this constriction is a highly dif- 

 ferentiated region which in my former paper ('14 a, p. 353) 



