MIDBRAIN AND THALAMUS OF NECTURUS 297 



eminentia subcerebellaris tegmenti. One of these is shown in 

 figure 35 and two of them are figured in my former paper ('14, 

 p. 25, fig. 18). Their axons have not been seen. 



The nucleus interpeduncularis. This is an area of very dense 

 neuropil lying ventrally of the ventral commissure from the tuber- 

 culum posterius far backward into the medulla oblongata. It is 

 not well developed rostrally of the fovea isthmi, but it becomes 

 large immediately caudad of that region. The neurons bor- 

 dering the extreme ventral part of the mesencephalic ventricle 

 send their dendrites downward through the fibers of the ventral 

 commissure. Here they branch freely, forming a compact 

 entanglement of bush}^ and thorn}^ dendritic branches, through 

 which slender unm3^elinated longitudinal axons descend into 

 the medulla oblongata (figs. 61, 68, 7iuc.ip.). These axons in 

 part are derived from the tractus habenulo-peduncularis and 

 in part they arise from the neurons of the interpeduncular nu- 

 cleus itself. 



VII. COXCLUSIOX 



This paper is concerned with the descriptive anatomy of 

 the midbrain and thalamus and their connections in Necturus. 

 The topography and subdivisions of the mesencephalon and 

 diencephalon are presented in Section II, and the internal 

 structure and functional connections of each of these regions 

 are given in Section VI. Some of these relations are show^n in 

 figures 62 to 68. These facts need not be again summarized 

 here. The specific morphological questions suggested by these 

 data can best be discussed at a later time after the functional 

 analysis of the amphibian diencephalon and telencephalon 

 has been more fully elucidated. Attention may be called here, 

 however, to some of the more general problems related to these 

 researches. 



Some of these questions have been suggested by the pre- 

 viously published studies of Coghill and the present writer on 

 the nervous system of Amblystoma. Coghill ('02) finds that 

 the functional components of the cranial nerves at about the 

 time of metamorphosis present the typical vertebrate pattern, 



