194 THE BRAIN OF THE TIGER SALAMANDER 



interpeduncular neuropil and especially within the interpeduncular 

 glomeruli (described below), of which they form an integral part. The 

 participation of specially modified ependyma in the formation of 

 these glomeruli raises interesting questions. There is no obvious de- 

 mand for unusual mechanical support here to account for especially 

 strong ependymal framework, except perhaps in the median raphe, 

 where the ependymal elements are more sturdy. Elsewhere in the in- 

 terpeduncular field the slender ependymal fibers branch freely, and 

 in the glomeruli they have tufted endings similar to those of den- 

 drites, to be described shortly. This elaboration of the ependymal 

 fabric within specialized synaptic fields suggests that the ependyma 

 has some part to play in metabolism at the synaptic junctions. 



INTERPEDUNCULAR NEUROPIL 



Ventrally of the interpeduncular gray and the commissure there is 

 a sharply circumscribed area of very dense superficial neuropil, oval 

 in cross-section, which in some of my published figures is marked 

 nuc.inp. It is preferable to apply the word "nucleus" to the gray area 

 only. This band of differentiated neuropil is, accordingly, currently 

 called the "specific interpeduncular neuropil" (inp.n. or nucinp.n.), 

 though it should be kept in mind that the entire interpeduncular 

 field is permeated by neuropil, of which this is a specialized part. Its 

 axonic component is a web of interlaced fibers, which is continuous 

 with that of surrounding parts. Imbedded within this fabric are two 

 specialized structures — the spiral terminals of the habenulo-inter- 

 peduncular tract and the glomeruli. The whole interpeduncular area 

 is richly vascularized with capillary net and is a synaptic field of great 

 importance. This activity evidently is especially concentrated in the 

 glomeruli and the area of specific superficial neuropil. 



The neuropil of the interpeduncular field is continuous dorsally 

 with the deep neuropil of the gray of the isthmic and trigeminal teg- 

 mentum and laterally with the intermediate neuropil of the alba of 

 these tegmental areas, as shown very inadequately in figures 60-66. 

 Posteriorly it is continuous with the diffuse neuropil which pervades 

 both the gray and the white substance of the medulla oblongata (figs. 

 79, 80, 81). In these drawings the structure of the neuropil is shown 

 greatly simplified and schematized, for it is impossible on this scale 

 of magnification to portray the intricacy of its texture. Since all 

 nerve fibers related with the interpeduncular system are unmyelinat- 

 ed and most of the tracts are dispersed in the neuropil, analysis is 



